Musannaf Ibn Abi Shaybah

Hazrat A'mash says that it was the practice of Hazrat Yahya bin Wathab to remain silent until the muezzin finished reciting the iqamah, and when he finished, he would say the opening takbeer (takbeer-e-tahreema). Whereas Ibrahim would say the takbeer when the muezzin recited "Qad qamatis salah."