Musannaf Ibn Abi Shayba 3:1715

Abu Mu'awiyah narrated to us, from Hisham, who said: Sufyan narrated to us, from al-A'mash, from Yahya ibn Waththab, who said: He used to remain silent until the mu'adhdhin finished, then he would say the takbir. And Ibrahim used to say: When he says "qad qamat al-salah" (the prayer has been established), say the takbir.