Musannaf Ibn Abi Shayba 27:883

Hatim narrated to us, from Humayd ibn Sakhr, from al-Maqburi, from Abu Hurayrah, who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "Whoever comes to this mosque of mine"—Abu Bakr said: meaning the mosque of Medina—"and does not come to it except for a good thing that he knows or learns, then he is in the position of the mujahid in the way of Allah. And whoever comes for other than that, then he is in the position of a man looking at the property of someone else."