Musnad Ahmad 1153:1652

Yahya narrated to us, from Hisham, who said: My father narrated to me, from Zaynab bint Abi Salamah, from Umm Salamah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "You bring your disputes to me, and perhaps some of you are more eloquent in their argument than others. I only judge for him according to what he says. So, whoever I judge for with something of his brother's right based on his statement, then I am only cutting for him a piece of the Fire, so let him not take it."