Sheikh Khâlid b. `Abd al-`Azîz al-Bâtilî, professor at al-Imâm University, Riyadh
The Prophet (peace be upon him) said: “Prescribed for the son of Adam is his portion of adultery which he must inevitably acquire. The adultery of the eyes is the glance. The adultery of the ears is listening. The adultery of the tongue is speech. The adultery of the hand is the grasp. The adultery of the foot is the step. The heart yearns and desires. The genitals then either confirm this or deny it.” [Sahîh al-Bukhârî and Sahîh Muslim]
This hadith means that a share of adultery will inevitably befall the sons of Adam. However, some of them will actually commit adultery by engaging in unlawful sexual intercourse and others will not. True adultery is to engage in outright sexual intercourse.
(Please note that when we refer to adultery in the context of this particular hadith, we mean both fornication and adultery.)
Those who do not actually commit adultery through outright sexual intercourse can still be said to do so in a figurative sense. This could be by looking at unlawful sights, by listening to sexual acts, by touching an unrelated woman with the hand, by kissing her, by walking somewhere with the intention of committing adultery, by engaging in illicit talk with a woman, or what have you. All of these can be considered adultery only in a figurative sense. Though such acts are sinful, they do not constitute adultery in a legal sense.
As for the phrase – "The genitals then either confirm this or deny it." – this means that the person who engages in these lesser acts will either follow through with them and actually engage in unlawful sexual intercourse, or he will restrain himself and avoid doing so.
And Allah knows best.
Source: Islam Today