Musnad Ahmad 28:538

'Abd al-Quddus ibn Bakr ibn Khunays Abu al-Jahm narrated to us, al-Hajjaj informed us, from 'Amr ibn Shu'ayb, from his father, from his grandfather, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every prayer in which [the Qur'an] is not recited is deficient, then deficient, then deficient."