Musnad Ahmad 27:1696

Abu al-Mughirah narrated to us, al-Awza'i narrated to us, 'Abdah ibn Abi Lubabah informed me, from 'Abdullah ibn 'Umar, who said: The Messenger of Allah, peace and blessings of Allah be upon him, took hold of a part of my body and said: "Worship Allah as if you see Him, and be in this world as if you were a stranger or a passerby."