From the perspective of Shia and Sunni Muslims, Imam Mahdi (AJ) will reappear in the end of the world and will fully spread justice in the world. The principle of the Dhuhur/Zuhur (reappearance) of Imam Mahdi (AJ) is a matter of course for all Islamic religions.

In some narrations, the circumstances of the reappearance and the events that preceded it have been briefly stated, but these matters have not been stated in such a way as to determine the exact time of the reappearance. In addition, it has been narrated from the Shia Imams (AS) as they say: “We do not set a time for reappearance and whoever does so; is a liar.”    

According to Shias and Sunnis, Imam Mahdi (A.J) will reappear in the end of the world and will fully spread justice and righteousness in the world and will remove oppression and infidelity, but there are differences between Shias and Sunnis regarding the details of his personality and the time of his reappearance.
In any case, the principle of the reappearance of Imam Mahdi (A.J) is a matter of course for all Islamic religions. It has been narrated from the Infallible Imams (A.S) as they say: “We do not set a time for reappearance and whoever determines it is a liar.”
For example, Fudayl ibn Yasar says that he said to Imam Baqir (A.S): “Is there a time set for the reappearance of Imam Mahdi (A.J)?” and he replied three times: “Those who set time for the reappearance, are lying.”

Of course, in some narrations, the conditions of the reappearance and the events that preceded it have been briefly stated, but expressing these matters is not in a way that determines the exact time of the reappearance.
In fact, the combination of these two groups of narrations, which, on the one hand, forbid determining the time of reappearance and, on the other hand, give a brief description of the conditions of it, is such that these brief circumstances of reappearance should be described in a way that does not lead to an exact determination of the time of reappearance and its UN justified application to similar peripheral examples should be avoided.

When we pay attention to the narrations that describe the circumstances of the reappearance, we also notice the same thing, none of which indicates the exact time of the reappearance.

source:shafaqna