Maslamah ibn Abi Bakr reported: Umar ibn Abdul Aziz, may Allah have mercy on him, took a pledge from some of his military deputies, saying, “You must fear Allah in every situation you find yourselves. Verily, the fear of Allah is greater for preparation, a better plan, and a stronger force. There is nothing of the hostility of your enemies that deserves more caution than your own selves and those with you who are sinfully disobedient to Allah. For I fear the sins of the people more than the plots of their enemies. Verily, we were only transgressed by our enemy and given divine support over them due to their sinful disobedience. Were it not for that, we would have no power over them.”
Source: Ḥilyat al-Awliyā’ 5/302
عَنْ مَسْلَمَةَ بْنِ أَبِي بَكْرٍ أَنَّ عُمَرَ بْنَ عَبْدِ الْعَزِيزِ رحمه الله عَهِدَ إِلَى بَعْضِ عُمَّالِهِ عَلَيْكَ بِتَقْوَى اللَّهِ فِي كُلِّ حَالٍ يَنْزِلُ بِكَ فَإِنَّ تَقْوَى اللَّهِ أَفْضَلُ الْعُدَّةِ وَأَبْلَغُ الْمَكِيدَةِ وَأَقْوَى الْقُوَّةِ وَلا تَكُنْ فِي شَيْءٍ مِنْ عَدَاوَةِ عَدُوِّكَ أَشَدَّ احْتِرَاسًا لِنَفْسِكَ وَمَنْ مَعَكَ مِنْ مَعَاصِي اللَّهِ فَإِنَّ الذُّنُوبَ أَخْوَفُ عِنْدِي عَلَى النَّاسِ مِنْ مَكِيدَةِ عَدُوِّهِمْ وَإِنَّمَا نُعَادِي عَدُوَّنَا وَنَسْتَنْصِرُ عَلَيْهِمْ بِمَعْصِيَتِهِمْ وَلَوْلا ذَلِكَ لَمْ تَكُنْ لَنَا قُوَّةٌ بِهِمْ
5/302 حلية الأولياء لأبي نعيم عمر بن عبد العزيز