Musannaf Ibn Abi Shayba 13:2488

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Zakariya narrated to us, from al-Sha’bi, that a man from Khath’am died in Daquqa, and no one witnessed his will except two Christians. Abu Musa made them swear after the afternoon prayer by Allah that they did not betray, nor conceal, nor alter, and that it was his will, and he permitted their testimony.