Musannaf Ibn Abi Shayba 13:1832

Abu Bakr narrated to us, he said: Ibn Mahdi narrated to us, from Hammad ibn Salamah, from Simak ibn Harb, from Abdullah ibn Shaddad, from Ibn Umar, that Umar wrote to Abu Musa regarding a man who drank wine: "If he repents, then accept his testimony."