Musnad Ahmad 1156:21

Abu Mu'awiyah narrated to us, he said: Hisham narrated to us, from his father, from Zaynab bint Abi Salamah, from Umm Salamah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "You bring your disputes to me, and it may be that some of you are more eloquent in their argument than others. I am only a human being; I judge in his favor according to what I hear from him. So, whoever I judge in his favor with something of his brother's right, it is only a piece of fire, so let him not take it."