Musnad Abu Ya'la al-Mawsili 152:7

Muhammad ibn Abdullah ibn Numayr narrated to us, Ibn Fudayl narrated to us, Asim narrated to us, from Awsajah ibn al-Rimmah, from Abdullah ibn Abi al-Hudhayl, from Abdullah ibn Mas’ud, who said: The Messenger of Allah, may Allah bless him and grant him peace, used to say: "O Allah, You have made my creation beautiful, so make my character beautiful."