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Narrated Jabir bin `Abdullah: While Allah's Messenger (ﷺ) was distributing the booty at Al-Ja'rana, somebody said to him "Be just (in your distribution)." The Prophet (ﷺ) replied, "Verily I would be miserable if I did not act justly."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا قُرَّةُ، حَدَّثَنَا عَمْرُو بْنُ دِينَارٍ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ ـ رضى الله عنهما ـ قَالَ بَيْنَمَا رَسُولُ اللَّهِ صلى الله عليه وسلم يَقْسِمُ غَنِيمَةً بِالْجِعْرَانَةِ إِذْ قَالَ لَهُ رَجُلٌ اعْدِلْ. فَقَالَ لَهُ " شَقِيتَ إِنْ لَمْ أَعْدِلْ ".
sunnah.com