What is the ruling on someone who prayed the obligatory prayer in his mosque, then came to another mosque to pray the funeral prayer, and found people praying the obligatory prayer there; should he join them with the intention of praying the obligatory prayer, or should he wait until they pray the funeral prayer?

Whoever prays in the mosque with a congregation is not required to repeat that prayer with another congregation as an obligation, but rather as a recommended act according to some scholars. Some others do not see repeating it at all. If one wishes to adopt this opinion, he may leave the mosque or wait in it until their prayer finishes, and then join them in the funeral prayer.