'God have mercy on him who knows his true state'

Umar b. Abd al-Aziz, the righteous Umayyad Caliph (d. 720), heard that one of his sons had purchased a diamond ring for one thousand dirhams. So Umar wrote to him, "I have heard that you have purchased a ring for one thousand dirhams; so when my letter reaches you, sell the ring, and feed one thousand starving souls, and get a ring made of iron for two dirhams, with the inscription, "God have mercy on him who knows his true state."