Hadith Qudsi 40
40) Narrated Anas bin Malik : We were in the company of Allah's Messenger when he laughed and said: Do you know why I laughed? The narrator said: We said: Allah and His Messenger know best. Then the Prophet said: I laughed at the talk of the slave to his Lord on the Day of Resurrection as he would say: 0 my Lord! Have You not guaranteed me protection against injustice? The Prophet said: Allah would say: Yes. The Prophet added: Then the slave would say: Today I do not allow any witness against me except a witness of my own self. Then the Prophet said: Allah would say: Today only yourself and the noble recording angels would be witnesses to you. Then the Prophet said: Then his mouth would be sealed and it would be said to his limbs: Speak. The Prophet added: They would speak of his deeds. He said: Then he would be made free to talk. The Prophet said: He would say to his limbs: Woe and curse be upon you. For only your sake I was contending.
This Hadith shows the controversial nature of man. Allah being All-Knower of this, will make man's own body parts witnesses for him.