Is it permissible for someone who has prayed the obligatory prayer alone to repeat it or interrupt it to join a congregational prayer?

Whoever prays the obligatory prayer alone is permitted to repeat it in congregation. And whoever begins an obligatory prayer alone, then the congregational prayer is established, is permitted to interrupt it and join the congregation, or to change his intention to a supererogatory prayer and complete it lightly, then join the congregation; this is recommended. If he fears missing the congregation, then he should interrupt his prayer and join the congregation. Interrupting the obligatory prayer here is not forbidden because it is an interruption to move to what is better.