Accordingto the explicit terms of that treaty, the caliphate of the Muslims was supposed to revert back to Imam Hasan (as) and, if Imam Hasan (as) had passed away, to Imam Husayn (as). So if Imam Husayn (as) had indeed been revolting against Yazid ibn Muawiya he would have been perfectly within his rights to do so. Forthe same reason there are NO mainstream sunnis who do not believe in the mahdi. To dispute the mahdi is to dispute the hadith, held by sunnis to be the words and deeds of the Prophet. Many things are similar between the 12th Imam and the Sunni Mahdi. The differenced should be pointed out in the article. For example, only Shia Hadith Mahdi(a.s.) is the one who will be present in the last era. The signs of Qiyamat will be apparent after his reappearance. This means that the reappearance of Imam Mahdi (a.s.) will be near to Qiyamat.". A similar narration is reported by Abdullah Ibne Masood from the Holy Prophet (s.a.w.a.). Sunniand Ahmadi are both sects within Islam, but they differ in their beliefs and interpretations. Sunni Islam is the largest branch of Islam, following the teachings and practices of the Prophet Muhammad, while Ahmadiyya is a relatively smaller sect that originated in the late 19th century, following the teachings of Mirza Ghulam Ahmad as the promised messiah and mahdi. SunniDocumentation on Imam al-Mahdi (as) Special specifications of Imam al-Mahdi (as) Imam Al-Mahdi's Identification. Also it is important to note that we do NOT believe that the parents of Prophets and Imams were necessarily perfect (Infallible). However we believe that their parents and all their forefathers were righteous and Imamat(and not wilayat of a philosopher as a deputee for Mahdi (pbuh) ) Resurrection (Paradise and Fire , and not enjoying the hell , or its vanishing ) In plus to the other ten pillars of islam . That is what makes you a shia , and not a believe that is clear to an extent it obligated even sunnis to believe in it : .

what do sunnis believe about imam mahdi