Ibn 'Abbas, radiyallahu 'anhu, said that the Messenger of Allah, sallallahu 'alayhi wasallam, said:
\"Were people to be given according to their claims, some would claim the wealth and blood of others. But the burden of proof is upon the claimant and the taking of an oath is upon the one who denies (the allegation).\" [An excellent hadith which al-Bayhaqi and others have related. Parts of it is in the two Sahih books (i.e. in al-Bukhari and Muslim).]