Musannaf Ibn Abi Shayba 3:450

Abu Bakr narrated to us, he said: Affan narrated to us, he said: Hammad ibn Salamah narrated to us, he said: Asim informed us, he said: Abu Wa'il entered upon me while I was ill, and I said to him: "Should I pray, O Abu Wa'il, while I am severely ill?" He said: "Yes."