Musannaf Ibn Abi Shayba 1:1472

Shababa narrated to us, he said: Shu'bah narrated to us, from Ghaylan ibn Jami', from Maymun ibn Mihran, who said: We were informed by one who saw Abu Hurayrah inserting his fingers into his nose, then he would bring out blood upon them, then he would rub it off. Then he would stand and pray.