According to rahyafte (the missionaries and converts website): From Sahih al-Bukhari: In this well-known Sunni hadith collection, there is a narration where Prophet Muhammad (peace be upon him) mentions the coming of Imam Mahdi: “If there were only one day left for the world to end, Allah would raise up a man from my family who would fill this earth with justice, just as it has been filled with injustice.” (Sahih al-Bukhari)
From Sahih Muslim: Another prominent Sunni hadith collection, Sahih Muslim, contains narrations regarding Imam Mahdi. One such narration states: “The world will not come to an end until a man from my family (the Ahlul Bayt) and of my name shall be master of the world, when the earth will be filled with injustice and tyranny.” (Sahih Muslim)
From Sunan Ibn Majah: This Sunni hadith collection includes references to the appearance of Imam Mahdi. One narration says, “The world will not come to an end until a man of the descendants of Fatimah (the daughter of the Prophet) shall be the Imam at the Kaaba. He will fill the earth with justice and equity as it is filled with injustice and tyranny.” (Sunan Ibn Majah)
From Musnad Ahmad ibn Hanbal: There are narrations in this collection that emphasize the return of justice and righteousness through Imam Mahdi. One narration mentions: “People will pledge allegiance to him (Imam Mahdi) between Rukn and Maqam (two important locations near the Kaaba), and an army will be sent against him from Syria. The army will be swallowed up in the desert between Mecca and Medina.” (Musnad Ahmad ibn Hanbal)
These Sunni narrations, among others, acknowledge the coming of Imam Mahdi and describe him as a figure who will bring justice, equity, and righteousness to the world. While there may be variations in the authenticity and interpretation of these narrations among Sunni scholars, the concept of Imam Mahdi is recognized and discussed in Sunni Islam.
