Musannaf Ibn Abi Shayba 3:3522

Abu Bakr narrated to us, he said: Abbad bin al-Awwam narrated to us, from al-Hajjaj, from a man, from Amr bin al-Harith bin Abi Dirar, from Umar bin al-Khattab regarding a man if he has a nosebleed during prayer: He said: He should turn away and perform ablution, then return and pray, and he should count what has passed.