Musnad Ahmad 109:2

Hassan ibn Musa narrated to us, Ibn Lahi'ah narrated to us, al-Harith ibn Yazid narrated to us, from Kathir al-A'raj al-Sadafi, who said: I heard Abu Fatimah, while he was with us at Dhu al-Awari, saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Abu Fatimah, increase in prostration, for there is no Muslim who prostrates a prostration to Allah, except that Allah raises him a degree by it."