Musnad Abu Ya'la al-Mawsili 209:2

Surayj ibn Yunus Abu al-Harith narrated to us, Yahya ibn Sa'id al-Umawi narrated to us, from Hisham ibn 'Urwah, from his father, from Zaynab bint Abi Salamah, from Umm Salamah, who said: I heard the Messenger of Allah (may Allah bless him and grant him peace) saying: "I am only a human being, and you bring your disputes to me. It may be that one of you is more eloquent in his argument than another, so I judge according to what I hear from him. Whoever I judge in his favor with something that belongs to his brother, let him not take anything of it, for I am only cutting out for him a piece of the Fire."