Musnad Ahmad 1302:38

Abu al-Yaman narrated to us, Safwan ibn 'Amr narrated to us, from Shurayh ibn 'Ubayd, from Abu al-Darda', that the Prophet, peace and blessings of Allah be upon him, said: "Indeed, Allah the Almighty and Majestic says: 'O son of Adam, do not be incapable of four rak'ahs at the beginning of the day, [and] I will suffice you for the end of it.'"