Musnad Ahmad 32:1983

Hajjaj al-A'war narrated to us, Shu'bah narrated to me, and Yazid ibn Harun said: Shu'bah informed us, from Qatadah, who said: I heard Anas ibn Malik saying: "The Prophet, peace and blessings of Allah be upon him, was among the lightest of people in prayer, while [still] completing it."