Musannaf Ibn Abi Shayba 3:2588

Abu Usama narrated to us, from Hisham, from Anas ibn Sirin, who said: I came with Anas ibn Malik from Kufa. When we were at Atat, the sky had overtaken us before that, and the ground was muddy. Anas prayed while he was on a donkey, facing the Qibla, and he gestured with a gesture, and he made the prostration lower than the bowing.