Musnad Ahmad 32:395

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Abu al-Tayyah, and Hajjaj said: I heard Shu‘bah, from Abu al-Tayyah, who said: I heard Anas ibn Malik narrating: "That the Messenger of Allah, peace and blessings of Allah be upon him, used to pray in the sheepfolds before the mosque was built."