Regarding this topic, Sheikh Muhammad Saleh Al-Munajjid, a prominent Saudi lecturer and author, stated:
There are more than one authentic hadith indicating that the Mahdi, may Allah be pleased with him, will appear at the end of time. His appearance is one of the portents of the Last Day. Among the hadiths are the following:
1- Abu Sa`eed Al-Khudri, may Allah be pleased with him, reports that the Messenger of Allah, peace and blessings be upon him, said: “At the end of the time of my Ummah, the Mahdi will appear. Allah will grant him rain, the earth will bring forth its fruits, he will give a lot of money, cattle will increase and the Muslim Ummah will become great. He will rule for seven or eight years.”
2- `Ali, may Allah be pleased with him, says: “The Messenger of Allah, peace and blessings be upon him, said: “The Mahdi is one of us and a member of my family. Allah will guide him in a single night.” (Reported by Ahmad)
3-Abu Sa`eed Al-Khudri states that the Messenger of Allah, peace and blessings be upon, said: “The Mahdi is of my lineage, with a high forehead and a long, thin, curved nose. He will fill the earth with fairness and justice as it was filled with oppression and injustice, and he will rule for seven years.” (Reported by At-Tirmidhi)
4- Jabir, may Allah be pleased with him, says that the Messenger of Allah, peace and blessings be upon him, said: ‘‘Jesus, son of Mary, will descend, and their leader, the Mahdi, will say, ‘Come and lead us in Prayer.’ But he will say, ‘No, one of them should lead them as an honor to this Ummah from Allah.” (Reported by Muslim)
We should be aware that some people have lied and fabricated hadiths about the Mahdi. Some of those “false Mahdis” have tried to deceive the servants of Allah for some worldly gain and distort the picture of Islam. Some have started movements and revolutions and gathered support from the people they deceived. But they were destroyed, and their lies and falsehood were exposed.