Musannaf Ibn Abi Shayba 21:355

Yahya ibn Adam narrated to us, Ammar ibn Ruzayq narrated to us, from Abu Ishaq, from al-Agharr Abu Muslim, from Abu Hurayrah and Abu Sa’id, both testifying to it from the Prophet, may Allah bless him and grant him peace, that he said: "No group of Muslims sits in a gathering in which they remember Allah, except that the angels surround them, mercy covers them, tranquility descends upon them, and Allah mentions them to those who are with Him."