Zayd bin Aslam (may Allah have mercy on him) said: I saw Abdullah bin Umar (may Allah be pleased with them both) praying in a blood-stained cloak. Nafi' (may Allah have mercy on him) came, removed the cloak from him and put his own cloak over him, and he continued in his prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4089