Musannaf Ibn Abi Shayba 3:2027

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Muhammad ibn Qays, from ‘Awn ibn ‘Abd Allah, from his father, who said: I prayed four [rak’ahs] with ‘Umar before the Dhuhr [prayer] in his house. And he said: "If you become confused, then be on the side of increase, and do not be on the side of decrease."