Musnad Ahmad 1156:154

'Abd al-Razzaq narrated to us, he said: Ma'mar narrated to us, from al-Zuhri, from 'Urwah, from Zaynab bint Abi Salamah, from Umm Salamah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) heard the clamor of disputants at the door of Umm Salamah. He went out to them and said: "You are disputing, and I am only a human being. It may be that some of you are more eloquent in their argument than others, so I judge in his favor according to what I hear from him, thinking him to be truthful. So, whoever I judge in his favor with something that belongs to his brother's right, it is a piece of the Fire; let him take it or leave it."