Musannaf Ibn Abi Shayba 3:2819

Ghassan ibn Mudar narrated to us, from Sa'id ibn Yazid, from Abu Nadra, who said: 'Uthman had become elderly. When he would ascend the pulpit, he would greet [the people] for a duration equal to what it takes a person to recite the Mother of the Book (Surah Al-Fatiha).