Is it permissible to combine the Maghrib and Isha prayers due to rain before the time for Isha begins?

The majority of scholars permit combining the Maghrib and Isha prayers at the beginning of the Maghrib time, if there is rain or its expectation. For the validity of combining them, the following conditions are stipulated:

1. Order between the two prayers (Maghrib then Isha).

2. Intention to combine, and the majority of scholars held that its place is at the time of declaring ihram for the first prayer, while some said it suffices during the prayer or upon finishing it.

3. Consecution between the two prayers.

Based on this, what the aforementioned Imam did is correct, and your prayer behind him is valid.