From Sahih Bukhari (Hadith 6243):
Narrated Ibn `Abbas:I have not seen a thing resembling 'lamam' (minor sins) than what Abu Huraira 'narrated from the Prophet who said "Allah has written for Adam's son his share of adultery which he commits inevitably. The adultery of the eyes is the sight (to gaze at a forbidden thing), the adultery of the tongue is the talk, and the inner self wishes and desires and the private parts testify all this or deny it
Reference: Bukhari 6243