Musnad Ahmad 31:731

And with this chain of narration, from the Messenger of Allah, peace and blessings of Allah be upon him, that he said: "The Lord, Mighty and Majestic is He, says: 'The people of the gathering will know today who are the people of nobility.'" It was said: "And who are the people of nobility, O Messenger of Allah?" He said: "The people of dhikr (remembrance of Allah) in the mosques."