Musannaf Ibn Abi Shayba 33:139

Abu al-Ahwas narrated to us, from Abu Ishaq, from a man from Juhaynah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The best of what a believer is given is a good character, and the worst of what a man is given is an evil heart in a beautiful form."