Musnad Ahmad 30:1727

Sulayman narrated to us, Isma'il informed us, al-'Ala' informed me, from his father, from Abu Hurayrah, that the Prophet, peace and blessings of Allah be upon him, said: "Hasten to [perform] deeds before tribulations [come] like pieces of the dark night; a man will wake up as a believer and go to sleep as a disbeliever, and he will go to sleep as a believer and wake up as a disbeliever, selling his religion for a small portion of the world."