Musnad Ahmad 935:5

Abu Kamil Muzaffar ibn Mudrik narrated to us, Zuhayr narrated to us, Abu Ishaq narrated to us, from Abdullah ibn Abi Basir, from his father, who said: I arrived in Medina and met Ubayy ibn Ka'b. I said: "O Abu al-Mundhir, narrate to me the most amazing hadith you heard from the Messenger of Allah, may Allah bless him and grant him peace." He said: The Messenger of Allah, may Allah bless him and grant him peace, led us—or led for us—the morning prayer. Then he turned his face toward us and said: "Is so-and-so present?" Then he mentioned the hadith.