Musannaf Ibn Abi Shayba 3:5951

Waki’ narrated to us, from Ja’far ibn Burqan, who said: Umar ibn Abd al-Aziz wrote to us during an earthquake that occurred in the Levant: "Go out on Monday of such-and-such month. Whoever among you is able to give charity, let him do so, for Allah the Exalted said: 'He has certainly succeeded who purifies himself, and mentions the name of his Lord and prays.'"