Musnad Abu Ya'la al-Mawsili 152:113

And from Jarir, from Asim al-Ahwal, from Awsajah ibn al-Rummah, from Abdullah ibn Abi al-Hudhayl, from Ibn Mas’ud, he said: The Messenger of Allah (may Allah bless him and grant him peace) used to say: "O Allah, You have made my creation excellent, so make my character excellent."