Umm Salamah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "I am only a human being, and you bring your disputes to me. Perhaps some of you may present his arguments more eloquently than others, so I judge in his favour according to what I heard. Whoever I judge in favour of with something of his brother's right should not take it, for I am only cutting off for him a piece of Hell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20531