Naim ibn Hammad and Abu Naim relate from Hazrat Ali (ra) by way of Mekhul that he said: I asked “O Messenger of Allah (saas), is Hazrat Mahdi (as one of us, from the line of Muhammad, or is he not one of us?” He replied: “No, he is certainly one of us. In the same way that Allah began this religion with me, so He will end it with him. And in the same way they were freed from polytheism through me, so they will be freed from strife by him. In the same way Allah installed love and friendship in people’s hearts and made them brothers in religion by freeing them from paganism and enmity through me, so He will free them from strife and enmity and make them brothers through Hazrat Mahdi (as).
Tabarani relates from Amr ibn Ali Tariqi and. Ali b. Ebi Talib in the Evsad: Hazrat Ali (ra) asked the Prophet (saas) “O Messenger of Allah, is Hazrat Mahdi (as) one of us, or is he not?” He replied: He is certainly one of us. In the same way Almighty Allah began Islam with me, so he will end it with him. In the same way that they were freed from polytheism and enmity AND FRIENDHSIP AND LOVE ENTERED THEIR HEARTS through me, SO IT WILL BE AGAIN (WITH THE COMING OF HAZRAT MAHDI [AS]). (Al-Muttaqi al-Hindi, Al-Burhan fi Alamat al-Mahdi Akhir az-Zaman, p. 23)
It is reported in the hadiths that Hazrat Mahdi (as) will eliminate all strife and division among Muslims, and will be instrumental in their becoming brothers by causing love and friendship to enter their hearts.