Musnad Ahmad 30:1275

Muhammad ibn Bishr narrated to us, Muhammad ibn ‘Amr narrated to us, Abu Salamah narrated to us, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am only a human being, and it may be that some of you are more eloquent in their argument than others. So, whoever I cut off a piece of his brother's right for, I have only cut off for him a piece of the Fire."