Sahih Muslim 1738
Sahih Muslim · Book 32: The Book of Jihad and Expeditions · The prohibition of betrayal
It is narrated on the authority of Abu Sa'id that the Messenger of Allah (ﷺ) said:
حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ ، حَدَّثَنَا عَبْدُ الصَّمَدِ بْنُ عَبْدِ الْوَارِثِ ، حَدَّثَنَا الْمُسْتَمِرُّ بْنُ الرَّيَّانِ ، حَدَّثَنَا أَبُو نَضْرَةَ ، عَنْ أَبِي سَعِيدٍ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لِكُلِّ غَادِرٍ لِوَاءٌ يَوْمَ الْقِيَامَةِ يُرْفَعُ لَهُ بِقَدْرِ غَدْرِهِ أَلاَ وَلاَ غَادِرَ أَعْظَمُ غَدْرًا مِنْ أَمِيرِ عَامَّةٍ " .
On the Day of Judgment there will be a flag for every person guilty of the breach of faith. It will be raised in proportion to the extent of his guilt; and there is no guilt of treachery more serious than the one committed by the ruler of men.