What is the ruling on performing Jumu'ah prayer twice in the same mosque, even though the imam is the same for both prayers?

If there is a need for multiple Friday prayers in the same mosque, and there is no imam other than the first imam, then there is no harm in him repeating the sermon and prayer. Some jurists have explicitly stated the permissibility of repeating the Friday prayer when multiple Friday prayers are allowed.

However, if there is no need for multiple Friday prayers, it is not permissible to repeat it, because the principle is that only one Friday prayer should be established in a town, unless there is a legitimate excuse.

If repeating the Friday prayer is permissible and there is an imam other than the first imam, then he should not repeat the Friday prayer twice, because repeating a fard (obligatory) prayer without a legitimate religious reason is not prescribed, and a fard prayer is only performed once, according to the Prophet’s (peace be upon him) saying: "Do not pray a prayer twice in one day."