Changing intention from praying alone to praying behind imaam during prayer
31-12-2017 | IslamWeb
Question:
Assalaamu alaykum. Suppose a man starts to pray the ‘Asr by himself. Then, after some time, a group of people come and start praying the ‘Asr together beside him, so the man is actually in the same row as the congregation. If that person changes his intention and follows the imam afterwards, is his prayer valid?
Answer:
All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
Scholars held different opinions regarding the validity of the prayer of a person who starts the prayer alone and then joins a congregation and follows the imaam. Some scholars held that his prayer is invalid because he changed his intention during the prayer and thus his intention was divided, while others held that his prayer is valid. Shaykh Ibn ‘Uthaymeen 
maintained that the correct view in this regard is that his prayer is valid. He said in his book Ash-Sharh Al-Mumti’, when commenting on the statement, “If a person praying alone changed his intention to praying behind an imaam...”:
“An example of this situation is when a person starts the prayer individually and then a group comes along and prays in congregation, so he changed from praying alone to praying behind the imaam who just arrived. His prayer is invalid because he has changed his intention during the prayer, so his intention is divided. He intended to pray individually at the beginning of his prayer and then changed the intention to pray behind an imaam. This is the same as changing his intention from one obligatory prayer to another (which invalidates the prayer). This is the view of our School of Fiqh. The second view was one of the reported opinions of Imaam Ahmad; that it is valid that the one praying alone changes his intention to praying behind an imaam because the difference here is in the description of the intention, not the intention itself. He was praying individually at first but then became led in prayer. It is not a change of the intention (to pray the same prayer) itself, so it is permissible. This is the correct opinion in this regard. They said: the evidence is that in the Sunnah, the validity of changing from praying alone to leading people in prayer was established, as will be explained later, Allah willing. So this indicates that such a change is of no effect (on the validity of prayer). Just as it is valid to change from praying alone to leading the prayer, it is also valid to change from praying alone to praying behind an imaam. There is no difference between the two cases; the only difference is that in the first case one leads the prayer, and in the second he is led.” [Ash-Sharh Al-Mumti’]
Hence, the prayer of this man, who changed his intention from praying alone to being led in the prayer with the congregation, was valid, Allah willing.
Allah knows best.