Short answer
Only in a limited way in the Hanafi school. Joining one or two people in a nafl prayer now and then is fine, but organising a congregation for voluntary prayers, with four or more followers gathered for it, is makruh, except for taraweeh, the eclipse prayer and the rain prayer. The Shafi'i and Hanbali schools allow nafl in congregation.
Nafl in congregation with tada'i, meaning people are called and gathered for it, is makruh; with one or two followers joining without invitation it is permissible. Taraweeh, the solar eclipse prayer and, for the two students, the rain prayer are the exceptions where congregation is sunnah. This includes group tahajjud, salat al-tasbih in congregation and group nafl on special nights.
Other madhhabs
- Shafi'i
- Nafl prayers may be prayed in congregation; it is permissible and not disliked, though some nafl are better alone.
- Maliki
- Nafl in congregation is allowed in a small group in a private place, and disliked in large gatherings or in the masjid where it may be taken as sunnah.
- Hanbali
- Nafl in congregation is permissible, as long as it is not made a regular practice.
Explanation
The Prophet ﷺ prayed at night in Ramadan in the masjid and people gathered behind him. After a few nights he stopped coming out, and told them: pray in your homes, for the best prayer of a person is in his home, except the obligatory prayer. At other times, Ibn Abbas joined his night prayer on his own, and the Prophet ﷺ moved him to his right side. Hanafi scholars combine these reports: a small, unplanned congregation for nafl is fine, while a gathering arranged for voluntary prayers is disliked, outside the prayers the Sunnah set for congregation.
What is fine in the Hanafi school:
- Taraweeh in congregation in Ramadan.
- The eclipse prayer for the sun.
- A spouse or child joining you in tahajjud now and then.
- Praying nafl individually in the masjid together on a special night, each person on his own.
What is makruh:
- Announcing a congregational tahajjud, salat al-tasbih or nafl on Shab-e-Barat or other nights, with an imam and rows of followers.
- Holding qiyam in congregation outside Ramadan as an organised event, in the view of most Hanafi scholars. Some later scholars allowed the last nights of Ramadan in congregation as an extension of taraweeh.
Gathering for Quran, dhikr and lessons on blessed nights is a separate matter. See is it better to pray sunnah at home, how to pray taraweeh and qiyam al-layl and tahajjud.
The evidence
Sahih al-Bukhari 731
Sahih... فصلوا أيها الناس في بيوتكم فإن أفضل الصلاة صلاة المرء في بيته إلا المكتوبة ...
"So pray, O people, in your homes, for the best prayer of a person is in his home, except the obligatory prayer."
The Prophet ﷺ stopped leading the night prayer in congregation and directed people to pray voluntary prayers at home.
Sahih al-Bukhari 117
Sahih... فقمت عن يساره فجعلني عن يمينه ...
"Ibn Abbas said: I stood on his left, and he moved me to his right."
One person joining a nafl prayer without invitation is fine.
Where the ruling is recorded
- al-Durr al-Mukhtar, Kitab al-Salah, chapter on witr and nawafil. Nafl in congregation with tada'i is makruh outside Ramadan; tada'i is four or more following one imam.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Salah, chapter on witr and nawafil. Discussion of the number that counts as tada'i and the exceptions.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.