Musnad Ahmad 28:175

Hassan narrated to us, Ibn Lahi'ah narrated to us, Rashid ibn Yahya al-Mu'afiri narrated to us, that he heard Abu Abd al-Rahman al-Hubuli narrating from Abdullah ibn Amr, who said: I said, "O Messenger of Allah, what is the spoils of the gatherings of remembrance?" He said, "The spoils of the gatherings of remembrance is Paradise, Paradise."