Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: Two men brought a case before the Prophet (peace and blessings be upon him), and the Prophet (peace and blessings be upon him) said: "I am only a human being. I judge between you according to what I hear from you. It may be that one of you is more eloquent in presenting his argument than his brother. So if I decide in someone's favour anything that belongs by right to his brother, I am only cutting off for him a piece of Hell."
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains al-Qasim bin Abdullah bin Umar, who is matruk (abandoned).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأحكام / 7023