Prayer: Doubting the Performance of Maghrib During Isha
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 746
If a person doubts during the ʿishāʾ prayer whether he has performed the maghrib prayer or not, he must complete the prayer with the intention of the ʿishāʾ prayer and after that perform the maghrib prayer. However, if the time is so little that after completing the prayer the time for prayers ends and there is not enough time remaining to perform even one rakʿah, it is not necessary to make up the maghrib prayer.