Is it permissible for me to join with the intention of Maghrib behind an imam who is praying 'Isha'?

Question : Is it permissible for me to join an imam who is praying 'Isha while I have the intention of Maghrib?

Answer : Yes. Perhaps you differ on two opinions, but in any case, it is permissible to pray in it. There are also two opinions among the scholars, or rather three. The first opinion is that it is not permissible for the ma'mum to pray behind an imam who differs from him in intention, even if the number of rak'ahs in the two prayers is the same. So it is not permissible to pray Zuhr behind one who is praying 'Asr. This is one.
The second opinion is that it is permissible to pray with an intention different from the imam's, even if the number of rak'ahs in the two prayers differs. The third opinion is that it is permissible for the intention of the imam and the ma'mum to differ if the number of rak'ahs in the two prayers is the same. So it is permissible to pray Zuhr behind one who is praying 'Asr because the number of rak'ahs in the two prayers is the same, but it is not permissible to pray Maghrib behind one who is praying 'Isha because the number differs. The correct view is that it is permissible, so the permissibility is the permissibility of differing in intention and number.