Sahih Muslim 155 f
The Book of Faith
The descent of 'Eisa bin Mariam to judge according to the Shari'ah of our Prophet (ﷺ) Muhammad (ﷺ); And how Allah has honored this Ummah; And clarifying the evidence that this religion will not be abrogated; and that a group from it will continue to adhere to the truth and prevail until the day of resurrection
It is narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) observed: What would you do when the son of Mary would descend amongst you and would lead you as one amongst you? Ibn Abi Dhi'b on the authority of Abu Huraira narrated: Your leader amongst you. Ibn Abi Dhi'b said: Do you know what the words:" He would lead as one amongst you" mean? I said: Explain these to me. He said: He would lead you according to the Book of your: Lord (hallowed be He and most exalted) and the Sunnah of your Messenger (ﷺ).