Musnad Ahmad 30:3292

Hajjaj narrated to us, he said: Ibn Jurayj said: Ziyad ibn Sa'd informed me that Salih, the freed slave of al-Taw'amah, informed him that he heard Abu Hurayrah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If a group of people sit in a gathering, then they stand up without remembering Allah in it, it will be a cause of regret for them on the Day of Resurrection."