Zina (adultery, fornication) does not refer only to penetration, rather there is the zina of the hand, which is touching that which is forbidden, and the zina of the eyes, which is looking at that which is forbidden, even though zina that is committed with the private parts, is the zina which is punishable with the hadd punishment. 

It was narrated from Abu Hurayrah that the Prophet (peace and blessings of Allaah be upon him) said: “Allaah has decreed for every son of Adam his share of zina, which he will inevitably commit. The zina of the eyes is looking, the zina of the tongue is speaking, one may wish and desire, and the private parts confirm that or deny it.”

Narrated by al-Bukhaari, 5889; Muslim, 2657. 

It is not permissible for the Muslim to long for the things that lead to zina, such as kissing, being alone, touching and looking, for all these things are haraam and lead to the greater evil which is zina. 

Allaah says (interpretation of the meaning): 

“And come not near to unlawful sex. Verily, it is a Faahishah (i.e. anything that transgresses its limits: a great sin, and an evil way that leads one to hell unless Allaah Forgives him)”

[al-Isra’ 17:32]

Looking at that which is forbidden is one of the arrows of the Shaytaan, which leads a person to doom, even if he did not do it intentionally at first. Allaah says (interpretation of the meaning): 

“Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts). That is purer for them. Verily, Allaah is All‑Aware of what they do.

And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts)”

[al-Noor 24:30-31]

Think about how Allaah connects the issue of lowering the gaze with the issue of protecting the private parts (guarding one’s chastity) in these verses, and how lowering the gaze is mentioned first, before protecting the private parts, because the eye influences the heart. 

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him) said: 

In these two verses, Allaah commands the believing men and women to lower their gaze and guard their chastity, which is because of the serious nature of zina and what it leads to of great corruption among the Muslims. Letting one's gaze wander freely is one of the causes of sickness in the heart and the occurrence of immoral actions, whereas lowering the gaze is one of the means of keeping oneself safe from that. Hence Allaah says (interpretation of the meaning): 

“Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts). That is purer for them. Verily, Allaah is All‑Aware of what they do.”

[al-Noor 24:30]

Lowering one’s gaze and guarding one’s chastity is purer for the believer in this world and in the Hereafter, whereas letting one’s gaze wander freely and not guarding one's chastity are among the greatest causes of doom and punishment in this world and in the Hereafter. We ask Allaah to keep us safe and sound. 

Allaah tells us that He is All-Aware of what people do, and that nothing is hidden from Him. This is a warning to the believer against doing that which Allaah has forbidden and turning away from that which Allaah has prescribed for him, and it is a reminder to him that Allaah sees him and knows all that he does, whether it is good or otherwise. As Allaah says (interpretation of the meaning): 

“Allaah knows the fraud of the eyes, and all that the breasts conceal”

[Ghaafir 40:19]

End quote. From al-Tabarruj wa Khataruhu. 

The Muslim has to fear his Lord in secret and in public, and keep away from that which Allaah has forbidden of being alone with a member of the opposite sex, looking, shaking hands, kissing and other haraam actions which lead to the immoral action of zina. 

The sinner should not be deceived into thinking that he will not commit zina and that he will stop at these haraam actions and not go that far, for the Shaytaan will never leave him alone. There is no hadd punishment for these haraam actions, such as kissing etc., because the hadd punishment is only for intercourse (zina), but the judge may punish him with a ta’zeer punishment to deter him and others like him from committing these sins. 

Ibn al-Qayyim said:  

Ta’zeer punishments may be prescribed for every sin for which there is no hadd punishment or specific expiation (kafaarah), for sins are of three kinds: those for which there is a hadd punishment but no kafaarah is required; those for which kafaarah is required but there is no hadd punishment; and those for which there is neither a hadd punishment nor kafaarah. The first type includes such crimes as stealing, drinking alcohol, zina and slander. The second includes having intercourse during the day in Ramadaan, or when in ihraam. The third type includes having intercourse with a slave woman who is owned jointly with someone else, kissing a non-mahram woman and being alone with her, entering the public baths without a waist wrapper, eating dead meat, blood and pork, and so on. 

I’laam al-Muwaqqa’een, 2/77 

The person who has committed any of these actions has to repent to Allaah, for whoever repents Allaah will accept his repentance, and the one who repents is like one who did not sin. 

One of the greatest means of expiation for such sins is offering the five daily prayers regularly and on time. The Prophet (peace and blessings of Allaah be upon him) said: “The five daily prayers, and from one Jumu’ah to the next, and from one Ramadaan to the next, expiates for the sins that come in between, so long as you avoid major sins.” Narrated by Muslim, 1/209 

And Allaah knows best.