Musnad Abu Ya'la al-Mawsili 117:169

Muhammad ibn Bakkar narrated to us, Buzi' Abu al-Khalil narrated to us, from Thabit, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever hears of a virtue from Allah and does not believe in it, he shall not attain it."