Musannaf Ibn Abi Shayba 28:599

Kathir ibn Hisham narrated to us, he said: Ja'far ibn Burqan narrated to us, he said: Thabit ibn al-Hajjaj al-Kilabi narrated to us, he said: Abu Bakr stood among the people, then he praised Allah and extolled Him. Then he said: "Beware, do not kill the monk in the hermitage."