ammarmali:

"A man once enquired of ‘Umar ibn ‘Abd al-‘Azīz, ‘When should I speak?’ And he replied, ‘Whenever you wish to remain silent.’ ‘And when should I be silent?’ the man asked, and Umar replied, ‘Whenever you wish to speak.’"

— Excerpt from Al-Ghazālī’s Iḥyā’ ‘ulūm al-dīn (The Revival of the Religions Sciences)