Umar on Treachery: I would kill a Muslim who betrays an unbeliever

Malik reported: A man from the people of Kufa said that Umar ibn al-Khattab wrote to a commander in an army he had dispatched, saying, “I have heard that it is the habit of some of your men to chase an unbeliever until he takes refuge in a high place. Then, a man tells him in Persian not to be afraid and when he comes down, they kill him. By him in whose hand is my soul, if I knew a man had done that once I would strike his neck.”

Ibn Abbas said, “People do not betray their covenants but that Allah will let their enemies overpower them.”

Source: al-Muwaṭṭa’ 951

عَنْ مَالِك عَنْ رَجُلٍ مِنْ أَهْلِ الْكُوفَةِ أَنَّ عُمَرَ بْنَ الْخَطَّابِ رضي الله عنه كَتَبَ إِلَى عَامِلِ جَيْشٍ كَانَ بَعَثَهُ إِنَّهُ بَلَغَنِي أَنَّ رِجَالًا مِنْكُمْ يَطْلُبُونَ الْعِلْجَ حَتَّى إِذَا أَسْنَدَ فِي الْجَبَلِ وَامْتَنَعَ قَالَ رَجُلٌ مَطْرَسْ يَقُولُ لَا تَخَفْ فَإِذَا أَدْرَكَهُ قَتَلَهُ وَإِنِّي وَالَّذِي نَفْسِي بِيَدِهِ لَا أَعْلَمُ مَكَانَ وَاحِدٍ فَعَلَ ذَلِكَ إِلَّا ضَرَبْتُ عُنُقَهُ

فَقَالَ أَنَّ عَبْدَ اللَّهِ بْنَ عَبَّاسٍ قَالَ مَا خَتَرَ قَوْمٌ بِالْعَهْدِ إِلَّا سَلَّطَ اللَّهُ عَلَيْهِمْ الْعَدُوَّ

951 موطأ مالك كتاب الجهاد باب ما جاء في الوفاء بالأمان