Is it permissible for someone who has prayed Maghrib alone at home to join a congregation praying Isha’ combined [with Maghrib] due to rain?

It is permissible to combine the Maghrib and Isha prayers due to rain if the interval between the two prayers is short, and one prays Isha with the congregation. However, if the interval is long, Isha is delayed until its prescribed time. The majority of jurists stipulate continuity between the two prayers, such that there is no long interval separating them, considering them as a single prayer. The measure of a short interval is determined by custom, and some jurists have estimated it to be the duration of the Iqama or ablution. Some jurists also stipulate the intention of combining the prayers at the beginning of the first prayer, contrary to the opinion of others. One must be keen to perform the prayer in congregation in the mosque, and if that is missed, then with the household members to attain the reward of congregational prayer.