Musnad Ahmad 404:1

Abdullah ibn Ahmad said: Abu Ahmad al-Haytham ibn Kharijah narrated to us, he said: Isma'il ibn 'Ayyash narrated to us, from Ishaq ibn 'Abdullah ibn Abi Farwah, from Yusuf ibn Sulayman, from his grandmother Maymunah, from 'Abd al-Rahman ibn Sannah, that he heard the Prophet, peace and blessings of Allah be upon him, saying: "Islam began as something strange, and it will return as something strange just as it began, so glad tidings to the strangers." It was said: "O Messenger of Allah, and who are the strangers?" He said: "Those who rectify when the people have become corrupt." "And by the One in Whose hand is my soul, faith will surely retreat to Medina just as a torrent retreats. And by the One in Whose hand is my soul, Islam will surely huddle between the two mosques just as a snake huddles into its hole."