The second is that he offers voluntary prayers during the intervals of rest in the tarawih prayer. We say: Do not offer voluntary prayers; hence he said, “It is disliked to offer voluntary prayers between them.”
His statement, “but not to resume prayer in congregation,” means that it is not disliked to resume congregational prayer after tarawih and witr. Resuming prayer means praying in congregation after them and after witr.
The apparent meaning of his words is that this applies even if it takes place in the mosque. For example, they pray tarawih and witr in the mosque, then say, “Come at the end of the night so that we may establish a congregation.” According to the author, this is not disliked. However, this view is weak, because it rests upon a report from Anas ibn Malik, may Allah be pleased with him, who said: “There is no harm in it; they are only returning to a good that they hope for …” (1) That is, do not return to prayer except for a good that you hope for.
But this report—if authentically established from Anas—conflicts with the Prophet’s ﷺ statement: “Make witr the last of your prayers at night.” (2) These people have prayed witr, so if they return to prayer afterward, witr will not have been the last of their night prayers. Therefore, the preponderant view is that the resumption of prayer described above is disliked. This is one of the two narrations from Imam Ahmad, may Allah have mercy on him. Both narrations are mentioned without preference in Al-Muqniʿ, Al-Furuʿ, Al-Fa’iq, and other works; that is, the two narrations from Imam Ahmad are regarded as equally established, with neither being given preference over the other.
However, if this resumption of prayer takes place after tarawih and before witr, then the view that it is not disliked is correct. This is the practice of the people today during the final ten