Umm Salamah reported the Messenger of Allah (ﷺ) as saying: "I am only a human being, and you bring your disputes to me, some perhaps being more eloquent in their plea than others, so that I give judgement on their behalf according to what I hear from them. Therefore, whatever I decide for anyone which by right belongs to his brother, he must not take anything, for I am granting him only a portion of Hell.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا سُفْيَانُ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ عُرْوَةَ، عَنْ زَيْنَبَ بِنْتِ أُمِّ سَلَمَةَ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِنَّمَا أَنَا بَشَرٌ وَإِنَّكُمْ تَخْتَصِمُونَ إِلَىَّ وَلَعَلَّ بَعْضَكُمْ أَنْ يَكُونَ أَلْحَنَ بِحُجَّتِهِ مِنْ بَعْضٍ فَأَقْضِيَ لَهُ عَلَى نَحْوِ مَا أَسْمَعُ مِنْهُ فَمَنْ قَضَيْتُ لَهُ مِنْ حَقِّ أَخِيهِ بِشَىْءٍ فَلاَ يَأْخُذْ مِنْهُ شَيْئًا فَإِنَّمَا أَقْطَعُ لَهُ قِطْعَةً مِنَ النَّارِ " .
sunnah.com