According to the Prophetic Sunnah, assembling in order to make dhikr (remembrance of Allah) is commendable. Specifying a certain day for gathering to offer Night Vigil Prayers is permitted by the majority of Muslim scholars except the Hanafis.
Focusing on this concept, the prominent Muslim scholar Sheikh Faysal Mawlawi, Deputy Chairman of the European Council for Fatwa and Research, issues the following fatwa: There are various texts in the Qur’an and the Sunnah showing that gathering to offer dhikr is commendable. Imam An-Nawawi (may Allah have mercy on him) wrote a whole chapter entitled “The Virtues of the Gatherings of Dhikr” in the book Riyad as-Salihin. In that chapter, An-Nawawi related four hadiths reported by both Al-Bukhari and Muslim to that effect, among them one that reads: Allah’s Messenger (may peace be upon him) went out to one of the gatherings of his Companions and said, “Why are you sitting like this?” They said, “We are sitting here in order to remember Allah and to praise Him for He guided us to the path of Islam and He conferred favors upon us.” Thereupon he adjured by Allah and asked if that only was the purpose of their sitting there. They said, “By Allah, we are not sitting here but for this very purpose.” Whereupon he (the Messenger) said, “I am not asking you to take an oath because of any allegation against you but for the fact that Gabriel came to me and he informed me that Allah, the Exalted and Glorious, was talking to the angels about your magnificence.” (Reported by Muslim) This is the proof for those who claim that such a deed is an innovation in religion.
Furthermore, it was related that the Prophet (peace and blessings be upon him) offered Night Vigil Prayers congregationally in a time other than Ramadan. Ibn Mas`ud said: “One night I offered the Tahajjud (Night Vigil Prayers) with the Prophet and he kept on standing till an ill thought came to me.” We said, “What was the ill thought?” He said, “It was to sit down and leave the Prophet (standing).” Similarly, Hudhaifa narrated: “I prayed with the Prophet (peace and blessings be upon him) one night and he started reciting Surat Al-Baqarah…” Then he went on describing the rest of the Prayers. Hence, how could it be said that such an assembly is considered to be an innovation in religion?
Moreover, although it was not reported that Allah’s Messenger (peace and blessings be upon him) appointed a certain day for offering the Night Vigil Prayers congregationally, yet appointing a day for it is approved of as long as this encourages people to observe that Prayer. In addition, that gathering cannot be regarded as an innovation because it is originally a practice in Islam, and because the majority of Muslim scholars said it is permissible except for the Hanafis.