Musnad Ahmad 32:2053

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from 'Abd al-'Aziz ibn Suhayb, he said: I heard Anas ibn Malik saying: "The Messenger of Allah (peace and blessings of Allah be upon him) used to make it (the prayer) brief and complete it," meaning he would lighten the prayer.