Musannaf Ibn Abi Shayba 3:464

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughirah, from Ibrahim, that when he would say the takbir, he would remain silent for a short while. And when he would say, "Not of those who have evoked [Your] anger or of those who are astray," he would remain silent for a short while. And when he would rise in the second rak'ah, he would not remain silent, and he would say, "All praise is [due] to Allah, Lord of the worlds."