Ibn Abbas, may Allah be pleased with him and his father, was asked: “Why does a traveller pray two rak'ahs when praying alone, but four when following a resident imam?” He replied: “That is the sunnah.” (1)

Issue: If a follower separates from the imam due to an excuse, then the excuse ceases, may he rejoin the imam, or should he continue praying alone? The jurists said: He may rejoin the imam, or he may continue praying alone. (2)

Thus, if we suppose that he separated and prayed one rak'ah, then rejoined his imam while the imam was still in the rak'ah in which he had separated from him, the imam will be one rak'ah behind him. When the imam stands to complete his prayer, the follower may sit and wait for him, or he may pray separately and complete his own prayer.

This sometimes occurs when the imam gives the salām before completing his prayer, and then the latecomer stands to make up what he missed. The imam is then told that he still has one rak'ah remaining, so he stands to complete that rak'ah. We say: The follower has now separated on the basis of the legal evidence, and is therefore excused for this separation. When the imam resumes in order to complete his prayer, the follower has a choice: if he wishes, he may continue his prayer; and if he wishes, he may rejoin the imam.

The fourth type is the transition from leading the prayer to praying alone. The author did not mention this, and it has two cases:

The first is when the follower’s prayer becomes invalid. For example, the congregation consists of an imam and one follower, and the follower’s prayer becomes invalid. In that case, the imam must transition from leading the prayer to praying alone, because his follower’s prayer has become invalid.