Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.126.
Section : On Looking into a Mirror.
‘Ali reported that when the Prophet, peace be upon him, looked into a mirror he would say, “Praise and thanks be to Allah. O Allah, make me good mannered as You made me good looking.” (Reported by Ibn As-Sinni) Anas reported that whenever the Prophet, peace be upon him, looked at his face in the mirror, he would say, “Praise be to Allah Who fashioned my nature and gave it a perfect form, and Who honoured my face and made it good, and made me one of the Muslims.”