Musannaf Ibn Abi Shayba 3:462

Abu Bakr narrated to us, he said: Isma'il ibn 'Ayyash narrated to us, from 'Amr ibn Muhajir, from 'Umar ibn 'Abd al-'Aziz, he said: He used to have two pauses: a pause when he said the takbir, and a pause when he finished the Mother of the Book (al-Fatiha).