Musannaf Ibn Abi Shayba 23:53

Ibn Numayr narrated to us, he said: Hisham narrated to us, from his father, from al-Miswar ibn Makhrama and Ibn Abbas: That they entered upon Umar when he was stabbed. He said: "The prayer." He said: "Indeed, there is no share in Islam for whoever neglects the prayer." So he prayed while his wound was gushing blood.