Abu Hurairah (RAA) narrated that the Messenger of Allah (ﷺ) said:
"If people sit in an assembly in which they do not remember Allah or invoke blessings on the Prophet it will be a cause of grief to them on the Day of Resurrection." Related by At-Tirmidhi who graded it as Hasan. (DE)
English reference (DE): Book 16, Hadith 1584 (DE)
Arabic reference (DE): Book 16, Hadith 1541 (DE)