Musnad Ahmad 31:545

'Affan narrated to us, Sulayman ibn Kathir narrated to us, al-Zuhri narrated to us, from 'Ata'—and 'Affan said once: 'Ata' ibn Yazid—from Abu Sa'id, who said: It was said, "O Messenger of Allah, which of the believers is best?" He said: "A believer who strives in the way of Allah with his self and his wealth." They said: "Then who?" He said: "A believer who isolates himself in a mountain pass, or a ravine, sparing the people from his evil."