Musannaf Ibn Abi Shayba 33:248

'Abdullah ibn Idris narrated to us, from Muhammad ibn Ishaq, from 'Asim ibn 'Umar, who said: 'Umar used to say, "Allah protects the believer." 'Asim ibn Thabit ibn al-Aflah had vowed that he would not touch a polytheist, and that no polytheist would touch him. So Allah protected him after his death, just as he had protected himself from them during his life.