Musannaf Ibn Abi Shayba 3:4916

Waki’ narrated to us, from Isra’il, from Hammad ibn Salamah, from Abu al-Bakhtari, from al-Hujaym: He said: I said to Abdullah ibn Rabah, "I see blood on my garment while I am in prayer." He said: "Continue in your prayer, and when you finish, wash it."