Musannaf Ibn Abi Shayba 3:5820

Waki’ narrated to us, from Sufyan, from Yahya ibn Abi Ishaq, who said: I heard Anas ibn Malik saying: We went out with the Prophet, may Allah bless him and grant him peace, and he shortened the prayer until we reached Mecca. He stayed there for ten days, shortening the prayer, until he returned to Medina.