Praying at graves and the conditions of intercession


A question answered by Shaikh Muhammad Salih Al-Munajjid regarding: “I was in a converstation with a follower of the sufi way of Islam and that person asked me what did I think about praying at the graves, or about religious scholars interceding during the day of judgement. I told that person that praying to someones grave is shirk and no one can interceed except the prophet. and I wanted to know what was the ruling of the people of knowledge on this matter and where can I look for proof ?".