Musnad Abu Ya'la al-Mawsili 152:237

Abu Khaythama narrated to us, Hashim ibn al-Qasim narrated to us, Shayban narrated to us, from Asim, from Zirr, from Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to fast three days from the beginning of every crescent moon, and he rarely would not fast on Friday.