Instructions for an officer sent to collect tax
Nahj al-Balāgha|Volume 1|Book 2|Chapter 26
آمَرَهُ بِتَقْوَى اللهِ فِي سَرَائِرِ أُمُورِهِ وَخَفِيَّاتِ عَمَلِهِ، حَيْثُ لَا شَهِيدَ غَيْرُهُ، وَلَا وَكِيلَ دُونَهُ.
He (Amīr al-mu’minīn) ordered him to fear Allāh in his secret matters and hidden actions, where there is no witness except He and no one watches save He.