Musnad Abu Ya'la al-Mawsili 42:431

From Abu Sa'id al-Khudri, from the Messenger of Allah (may Allah bless him and grant him peace), who 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: "And who are the people of nobility?" He said: "The people of dhikr (remembrance of Allah) in the mosques."