[ English - إنجليزي ]
“…No person earns any (sin) except against himself (only), and no bearer of burdens shall bear the burden of another…” (Quran 6:164)
“The fathers shall not be put to death for the children, neither shall the children be put to death for the fathers: every man shall be put to death for his own sin.” (Deuteronomy 24:16)
None can reject that in these two verses, the first from the Quran and the second from the Bible, is an allusion to the same meaning: that the Just God will never punish people for the sins of others.
Christianity alleges that God created humans to live eternally in Heaven, and that when Adam ate from the tree from which he had been forbidden, God punished him through death and banishment from Heaven. They further assert that as death was inherited by his progeny, so too was the sin of their father, which was a permanent stain on the hearts of humanity, never to be removed except through a sacrifice so great that it would oblige God to forgive humanity. This sacrifice would be nothing other than the sacrifice of God himself, incarnate in His “son” Jesus. Therefore Christianity deems all of humanity as damned to Hell for the sin of Adam from which they could never be cleansed, except through the belief that God became incarnate and died for Adam’s sin, ritualized as Baptism, through which Christians are ‘born again’ into the world, but this time free of sin.  So we see that the theory of ‘Original Sin’ forms the basis of various Christian beliefs, from the crucifixion of Jesus to the concept of salvation and savior from Hell. It forms the very basis for the mission of Jesus himself.
So the questions arise, is humanity guilty for the sin which Adam committed by eating from the tree he was forbidden? Must we all repent from that great sin? In what way is one to repent? And if so, what is the fate of those who did not?
Islam strictly promotes the notion that the punishment of sins will only be faced by those who commit them. Sin is not a hereditary trait or ‘stain’ passed to one’s progeny one generation to another. All people will be accountable to what only they themselves did in this life. Therefore, even though the Quran mentions the sin of Adam and how he was banished from the Garden, it places no responsibility on the shoulders of his progeny. None of the Prophets before Jesus were known to have preached this concept, nor were any other beliefs or rituals based upon this belief. Rather, salvation from Hell and attainment of Paradise was achieved through the belief in One God and obedience to His commandments, a message preached by all prophets, including Muhammad, may the mercy and blessings of God be upon him, as well.
As for the sin of Adam, the Quran tells us that he repented for his sin. God revealed to him words with which to repent, which he then accepted from him.
“Then Adam received Words (of forgiveness) from his Lord, and he accepted his repentance. Verily, He is the One Who repeatedly accepts repentance, the Most Merciful.” (Quran 2:37)
Through God’s acceptance of Adam’s repentance, Adam was cleansed of the sin which he committed. God in the Quran repeatedly ascribes to Himself attribute of mercy and forgiveness. He also mentions that from His Names are The Oft-Forgiving, The Most Merciful, the Accepter of Repentance, and others, all of which emphasize the All-Encompassing Mercy of God. Even to those who have sinned much and may lose hope in the forgiveness of God, He says:
“Say: ‘O My slaves who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of God, indeed God forgives all sins. Truly, He is Oft-Forgiving, Most Merciful.’” (Quran 39:53)
If a person sins, all they need to do is truly repent from their heart, and they will find God Ever Merciful. Adam did sin, and the sin did stain his heart, but it was removed through his repentance. The Prophet Muhammad said:
“Indeed if a believer sins, a black spot covers his heart. If he repents, and stops from his sin, and seeks forgiveness for it, his heart becomes clean again. If he persists (instead of repenting), it increases until covers his heart…” (Ibn Maajah)
Even if we were to say that Adam did not repent, that stain is not passed on to further generations. Therefore, we see that God does not need any physical sacrifice in order to forgive sins, and that no sin is too great for His Mercy; to say so would be to ascribe deficiency to His Excellence and Perfection. The Prophet Muhammad relates to us that God said:
“O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you. O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to face Me, ascribing no partner to Me, I would bring you forgiveness nearly as great at it.” (Al-Tirmidhi)
God says in the Quran in regards to sacrifice, that it is the intention of the person when offering the sacrifice which is of importance, and not the actual sacrifice itself.
“It is neither their meat nor their blood that reaches God, but it is piety from you that reaches Him...” (Quran 22:37)
If we were to implement this verse in regards to the original sin and God incarnate sacrificing himself in order to forgive all of humanity, we see that even without seeking repentance for Adam’s sin, God forgave human beings due to His Own Sacrifice. Could He not have forgiven them without such a sacrifice?
It is also mentioned in the bible:
“To what purpose (is) the multitude of your sacrifices unto me? Saith the LORD: I am full of the burnt offerings of rams and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats. When ye come to appear before me, who hath required this at your hand, to tread my courts? Bring no more vain oblations; incense is an abomination unto me; the new moons and Sabbaths, the calling of assemblies, I cannot away with; (it is) iniquity, even the solemn meeting. Your new moons and your appointed feasts my soul hateth: they are a trouble unto me; I am weary to bear (them). And when ye spread forth your hands, I will hide mine eyes from you: yea, when ye make many prayers, I will not hear: your hands are full of blood. Wash you, make you clean; put away the evil of your doings from before mine eyes; cease to do evil; Learn to do well; seek judgment, relieve the oppressed, judge the fatherless, plead for the widow. Come now, and let us reason together, saith the LORD: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.” 
So Adam sought forgiveness for His sin, and God accepted it from Him. Another crucial point which must be mentioned is that God created humans with a free will, and He knew that humanity would sin. For this reason, no human is expected to be perfect, but rather, God knows that they will sin. What is expected from humans is that they repent from their sin. The Prophet, may the mercy and blessings of God be upon him, said:
“All children of Adam repetitively make mistakes, but the best of those who make mistakes are those who repent.” (Ibn Maajah)
The Prophet also said:
“By Him in Whose Hand is My soul (i.e. God), if you did not commit sins, God would do away with you and come with a race which committed sins. They would seek forgiveness from God and He would forgive them. (Saheeh Muslim #4936)
So here we see that it was in the Great and Wise plan of God that Adam sin and that God forgive him for that sin, and to say that Adam went against the Universal Will of God by sinning is a blasphemy against the All Encompassing Knowledge, Power, and Will of God. Christianity goes so far as to say that God even repented from the creation of humans! May God be free from all defects people attribute to Him. In Genesis 6:6, it says to quote:
“And it repented the Lord that he had made man on the earth, and it grieved him at his heart” 
To agree to this would mean that Adam did something which was out of the Will, Power, and Knowledge of God, and that God regretted His creation of humans. God is All-Perfect and so are His deeds, and there is no defect or shortcoming in them; He does nothing except with total and complete perfection and wisdom. Islam in no way agrees to this belief and, as we mentioned, all of what occurred in the story of Adam was within the perfect plan of God. The Prophet said:
“Indeed God put everything into its proper measure fifty thousand years before the creation of the heavens and the earths.” (Al-Tirmidhi)
God mentions in the Quran what took place between the angels when He announced the creation of humans, and from this we see that it was known to God and part of His Great and Divine Plan that humans would sin. God says:
“And (remember) when your Lord said to the angels: ‘Verily, I am going to place (mankind) generations after generations on earth.’ They said: ‘Will You place therein those who will make mischief therein and shed blood, - while we glorify You with praises and thanks and sanctify You.’ He (God) said: ‘Indeed I know that which you do not know.’” (Quran 2:30)
It is also clear from these verses that God did not create humans as immortal, and that death was prescribed for them from the beginning of their creation. As for the consequences of the sin of Adam, which was his extradition from the Garden, this was felt by those to come after him and this is only natural. If one was to become drunk and have a car accident, and some of the passengers die, the sin of driver effects the passengers in their death, but that does not mean that the passengers are to be held to account for the sin of the driver.
Another question which must be dealt with is the fate of those who came before the claim that God became incarnate and sacrificed himself for the sins of humanity, as well as the fate of those who were not baptized, as baptism is the rite which all Christians must perform in order to be cleansed of Original Sin. In Christian belief, all humans previous to the incarnation of God, including the Prophets and infants usually regarded as sinless, are not free from the Original Sin of Adam, and therefore cannot enter the Kingdom of Heaven, As Augustine said: “Do not believe, nor say, nor teach, that infants who die before baptism can obtain the remission of original sin.”  Only until recently, non-baptized infants were not buried in consecrated ground because they were believed to have died in original sin.
Also, we know that the verse in the Apostles’ Creed, “… and (Jesus) descended into Hell” , is said to mean that Jesus descended to Hell to free the righteous souls who were there due to the sin of Adam. This leads us to believe that all those before the coming of Jesus are in Hell, even if they were from the righteous. Paul mentioned this himself in Galatians:
“… a man is not justified by the works of the law ... for by the works of the law shall no flesh be justified.” (Galatians 2:16)
Here it is clear that adherence to the commandments of God is not enough for salvation, even for those before Jesus. This also holds true to all those who have not received the message of Christianity. We must ask; why did not the Prophets before Jesus call to this notion of original sin? Did they lie when they said that it was enough to Worship One God and obey His commandments to achieve Paradise? Why did not God come and free humanity from sin at the time of Adam so that the righteous and others would not be in Hell due to his sin? Why are infants, humanity before Jesus, and others who have not heard about Christianity, held accountable for a sin they never committed, nor have knowledge about how to remit themselves from it? The truth of the matter is that the notion of “Original Sin”, as many others, was one introduced by Paul and later expounded on by Christian scholars and councils.
“The Old Testament says nothing about the transmission of hereditary sin to the entire human race… the main scriptural affirmation of the doctrine is found in the writings of St. Paul…”
This concept though, was expounded by Augustine of Hippo, one of the most prominent Christian scholars in History. The basis of this concept is that “the deliberate sin of the first man (Adam) is the cause of original sin.”  The Second Council of Orange (529 C.E.) declared, “One man has transmitted to the whole human race not only the death of the body, which is the punishment of sin, but even sin itself, which is the death of the soul.” 
The concept of original sin is one which has no basis in previous scriptures regarded as divine by Christianity. None of the Prophets before Jesus were known to have preached this concept, nor were any other beliefs or rituals based upon them. Rather, salvation from Hell was achieved through the belief in One God and obedience to His commandments which was preached by all prophets, including the Prophet of Islam, Muhammad, may God praise them.
In Islam, the key to salvation is the belief in and worship of the One True, Unique and Perfect God and obedience to His commandments, the same message brought by all Prophets. Islam preaches that a person must work righteousness and avoid sin to attain Paradise, and that if one sins, that they seek repentance for it from their heart. Through this and the Mercy and Grace of God, they will enter Paradise. Islam does not deem that all those before the advent of Muhammad are doomed to Hell, but rather that each nation was sent a prophet by the same One God, and it was upon them to follow His commandments. Those who have not heard of the message are not held liable to follow Islam, and God will deal with them with His Perfect Justice on the Day of Judgment. Infants and children of both Muslims and disbelievers alike are in enjoyment in Paradise upon death. Due to the infinite Justice of God:
“No one laden with burdens can bear another’s burden. And We never punish (people) until We have sent (to them) a Messenger (to give warning).” (Quran 17:15)
 Apol., I, Ixvi.
 Isaiah 1:11-18
 King James Version.
 De Anima (III).
 The creed based on the Catechism of the Council of Trent.
 Merriam-Webster’s Encyclopedia of World Religions. P.830. 1999, Merriam Webster, inc.
 De Nuptiis et Concupiscentiâ, II, xxvi, 43
 Enchiridion Symbolorum, Heinrich Joseph Dominicus Denzinger. n. 175 (145)