Musannaf Ibn Abi Shayba 3:4909

Hatim ibn Wardan narrated to us, from Bard, from Nafi’, from Ibn Umar, that when he was in prayer and saw blood on his garment: If he was able to remove it, he would remove it. And if he was not able to remove it, he would exit and wash it, then he would come back and continue from what he had already prayed.