Riyad as-Salihin

Abu Hurairah and Abu Sa'id Al-Khudri (May Allah be pleased with them) reported: The Messenger of Allah (ﷺ) said, "When a group of people assemble for the remembrance of Allah, the angels surround them (with their wings), (Allah's) mercy envelops them, Sakinah, or tranquillity descends upon them and Allah makes a mention of them before those who are near Him."

[Muslim].