Sahih Muslim Book 1, Hadith Number 272.

Chapter : Islam was initiated as something strange, and it would revert to its (old position) of being strange, and it would concentrate between the two mosques.

It is narrated on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) said: Verily the faith would recede to Medina just as the serpent crawls back into its hole.