Musnad Ahmad 8:165

Harun ibn Ma'ruf narrated to us, Abdullah ibn Wahb informed us, Abu Sakhr informed me—Abu Abd al-Rahman Abdullah ibn Ahmad said: And I heard it myself from Harun—that Abu Hazim narrated to him, from a son of Sa'd ibn Abi Waqqas, who said: I heard my father saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, while he was saying: "Indeed, faith began as something strange and it will return as it began. So glad tidings on that day for the strangers when the people become corrupt." "And by the One in Whose hand is the soul of Abu al-Qasim, faith will certainly retreat between these two mosques just as a snake retreats into its hole."