Musnad Ahmad 1153:383

Aswad narrated to us, Isra'il narrated to us, from 'Asim ibn Sulayman, from 'Abdullah ibn al-Harith, from 'Aishah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to say: "O Allah, You have made my creation excellent, so make my character excellent."