It was reported from the Messenger of Allah ﷺ that he heard a dispute at the door of his chamber, so he went out to them and said, "I am only a human being. Disputants come to me, and perhaps one of you is more eloquent than the other, so I assume he is telling the truth and rule in his favor accordingly. Whoever I rule in favor of with something belonging to a Muslim by right, it is only a piece of the Fire, so let him take it or leave it."
عن رسول الله ﷺ: أنه سمع خصومة بباب حجرته، فخرج إليهم، فقال: إنما أنا بشر، وإنه يأتيني الخصم، فلعل بعضكم أن يكون أبلغ من بعض، فأحسب أنه صدق فأقضي له بذلك، فمن قضيت له بحق مسلم، فإنما هي قطعة من النار فليأخذها أو فليتركها.
Bukhari narrated it in the Book of Injustices (2458), and Muslim in the Book of Judgments (1713), both from the hadith of Ibn Shihab Zuhri, who said, Urwa bin Zubayr informed me, that Zaynab bint Umm Salama informed him, that her mother Umm Salama, the wife of the Prophet ﷺ, informed her, and mentioned it.