Musnad Abu Ya'la al-Mawsili 152:145

From Waki’, from Sufyan, from ‘Abdullah ibn al-Sa’ib, from Zadhan, from ‘Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah has angels who travel about the earth, conveying to me the greeting of peace (salam) from my Ummah."