Musannaf Ibn Abi Shayba 3:463

Abu Bakr narrated to us, he said: Affan narrated to us, he said: Hammad ibn Salamah narrated to us, from Humayd, from al-Hasan, from Samurah ibn Jundab, from the Prophet (may Allah bless him and grant him peace): He 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."