The greatest fault is to find fault in another with what is also in you.
أكبر العيب أن تعيب ما فيك مثله
Akbar al-ʿayb an taʿība mā fīka mithluhu
Ali, Nahj al-Balagha, saying 353 (Subhi Salih edition, p. 536; saying 353 in the Abduh edition). The Nahj al-Balagha is a compilation without chains of transmission by al-Sharif al-Radi (d. 1015).
It is easy to see another's flaw.
Hard to see your own.
Ali names the greatest fault:
finding fault in another with what is in you.
Most of the time
what angers us most in another
is our own mirror.