The descent of Prophet ‘Isa (As) and the coming of the Mahdi are subjects “that cannot be denied” in the faith (itiqad) of the people of the people of the sunnah.
According to the beliefs of the people of the Sunnah (the Hanafi, Hanbali, Shafi’i and Maliki schools), the coming of the Mahdi, the descent from the skies of the Prophet ‘Isa (as) and his bestowing the role of imam on the Mahdi are all unquestionable tenets of faith.
In this site you may find some trustworthy hadith regarding the coming of the prophet Isa (As) and the blessed Mahdi.