Musannaf Ibn Abi Shayba 17:1346

Ibn Numayr narrated to us, he said: Hisham ibn Urwah narrated to us, from his father, from Abu Marwah, from Abu Dharr, who said: I said, "O Messenger of Allah, which deeds are best?" He said, "Faith in Allah and Jihad in His cause." I said, "Which necks (slaves) are best?" He said, "The most precious of them to their owners and the most expensive of them in price." I said, "If I cannot do that?" He said, "You assist one who is lost, or you work for one who is unskilled." I said, "If I am not able?" He said, "Then refrain from harming people, for it is a charity you bestow upon yourself."