Musnad Abu Ya'la al-Mawsili 42:73

Ahmad ibn Isa narrated to us, Ibn Wahb narrated to us, Amr narrated to us, from Abu al-Samh, from Abu al-Haytham, from Abu Sa’id, from the Messenger of Allah, may Allah bless him and grant him peace, that he said: The Lord will say on the Day of Resurrection: "The people of the gathering will know today who are the people of nobility." It was said: "Who are the people of nobility, O Messenger of Allah?" He said: "The gatherings of dhikr (remembrance) in the mosques."