Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6220
This hadith has been transmitted on the authority of Abu Huraira with some addition (and it is this):" Verily Allah does not look to your bodies nor to your faces but He looks to your hearts," and he pointed towards the heart with his fingers.