Musnad Ahmad 799:166

'Affan narrated to us, Hammad ibn Salamah narrated to us, from Humayd, from al-Hasan, from Samurah ibn Jundub: "The Messenger of Allah (peace and blessings of Allah be upon him) used to remain silent for two silences: when he entered into the prayer, and when he finished the recitation." 'Imran ibn Husayn denied that, so they wrote to Ubayy ibn Ka'b. He wrote back to them: "Samurah has spoken the truth."