Musannaf Ibn Abi Shayba 2:52

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from Zubayd, from Khaythama, who said: They used to perform the *tathwib* (calling out "as-salatu khayrun min an-nawm") in the *Isha* and the *Fajr* prayers.