A man entered with the imam while he was praying the night prayer, and the man had not prayed the 'Isha' prayer, so he caught one rak'ah, then the imam said the taslim, so the man stood up and prayed one rak'ah and completed the two rak'ahs

The questioner : May Allah bless you. A man entered the mosque and the imam was leading the people in the night prayer, so he caught the second rak'ah with him, intending the 'Isha' prayer. Then when the imam said the taslim, he stood up and performed another rak'ah, then he followed the imam in the other two rak'ahs, then he said the taslim with the imam. Is his prayer valid?

The Shaykh : No, he was required to pray three rak'ahs, yes, on his own, because this means that he changed his intention during the prayer, and this invalidates the prayer.

The questioner : Is it obligatory for him to repeat it?

The Shaykh : Yes, exactly.

The questioner : May Allah reward you.

The Shaykh : And to you.