Musnad Ahmad 799:50

'Affan narrated to us, Yazid bin Zuray' narrated to us, Yunus narrated to us, from al-Hasan, from Samurah, who said: "When he (the Prophet) would say the Takbir, he would remain silent for a brief moment, and when he finished reciting the Surah, he would remain silent for a brief moment." 'Imran bin Husayn disapproved of that, so they wrote to Ubayy bin Ka'b, and Ubayy wrote back confirming him (Samurah) to be truthful.