If a latecomer misses the 'Isha' prayer, should he pray the Tarawih prayer with the Imam then perform the 'Isha' prayer alone, or should he pray the Qiyam prayer with the Imam?

The scholars have differed regarding someone praying 'Isha' behind someone praying Taraweeh. The majority held that the prayer is not valid due to the difference in intention. However, the Shafi'is maintained the validity of his prayer and his attainment of the virtue of congregational prayer, and this is the more preponderant opinion, because the difference in intention is not a factor. This is based on what was reported about Mu'adh, who used to pray 'Isha' with the Prophet, then return and lead his people in that same prayer, which would be a supererogatory prayer for him and an obligatory prayer for them. The Prophet approved of this. Therefore, if someone misses the 'Isha' prayer and finds the Imam praying Taraweeh, he should join him with the intention of praying 'Isha' to gain the virtue of congregational prayer.