Musnad Ahmad 32:31

Muhammad ibn Abd al-Rahman al-Tafawi narrated to us, Ayyub narrated to us, from Abu Qilabah, from Anas ibn Malik, from the Prophet, may God bless him and grant him peace, who said: "When dinner is served and the prayer is established, begin with dinner." And the Messenger of God, may God bless him and grant him peace, said: "If one of you becomes drowsy during his prayer, let him leave and sleep."