Musnad Abu Ya'la al-Mawsili 108:32

'Abd Allah ibn Mas'ud entered the mosque while the Prophet, may Allah bless him and grant him peace, was delivering the sermon. He sat next to Ubayy ibn Ka'b and asked him about something, or spoke to him about something, but Ubayy did not reply to him. Ibn Mas'ud thought that it was out of resentment. When the Prophet, may Allah bless him and grant him peace, turned away from his prayer, Ibn Mas'ud said, "O Ubayy, what prevented you from replying to me?" He said, "You did not attend the Friday prayer with us." He said, "Why?" He said, "You spoke while the Prophet, may Allah bless him and grant him peace, was delivering the sermon." Ibn Mas'ud stood up and entered upon the Prophet, may Allah bless him and grant him peace, and mentioned that to him. The Messenger of Allah, may Allah bless him and grant him peace, said, "Ubayy has spoken the truth. Obey Ubayy."