Instructions for an officer sent to collect tax
Nahj al-Balāgha|Volume 1|Book 2|Chapter 26
وَإِنَّ أَعْظَمَ الْخِيَانَةِ خِيَانَةُ الْأُمَّةِ، وَأَفْظَعَ الْغِشِّ غِشُّ الْأَئِمَّةِ، وَالسَّلَامُ.
Surely, the greatest treachery is the treachery against the Muslim community, and the ugliest deceit is the deceit towards the Muslim leaders; and that is an end to the matter.