Musnad Abu Ya'la al-Mawsili 151:8

Uthman ibn Abi Shaybah narrated to us, Ghundar narrated to us, from Shu'bah, from Mughirah, from Shibak, from Ibrahim, from Hani ibn Nuwayrah, from Alqamah, from Abdullah, from the Prophet (peace and blessings of Allah be upon him), who said: "The most restrained of people in killing are the people of faith."