Sahih Muslim Book 1, Hadith Number 290.

Chapter : The descent of Jesus son of Mary, and he will judge according to the Shari’ah of our Apostle, Muhammad(may peace be upon him).

It is narrated on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) observed: What will be your state when the son of Mary descends amongst you and there will be an Imam amongst you?