Mishkat al-Masabih 86

Abu Huraira reported God's messenger as saying, “God has decreed for man his portion of fornication which he will inevitably commit. The fornication of the eye consists in looking, and of the tongue in speech. The soul wishes and desires, and the private parts accord with that or reject it.” (Bukhari and Muslim.) In a version by Muslim he said, “Man’s share of fornication which he will inevitably commit is decreed for him. The fornication of the eyes consists in looking, of the ears in hearing, of the tongue in speech, of the hand in violence, and of the foot in walking. The heart lusts and wishes, and the private parts accord with that or reject it.”