Musnad Ahmad 1603

It was narrated that a son of Sa"d bin Abi Waqqas said: I heard my father say: I heard the Messenger of Allah (ﷺ) say: "Faith began as something strange and will go back to being as it began, so glad tidings to the strangers when the people become corrupt. By the One Whose hand is the soul of Abul-Qasim, faith will retreat between these two mosques as a snake retreats into its hole.”