Valentine’s Day is actually celebrated in memory of a Christian priest. Allah SWT has warned of hurtful punishment.
As given in (Surah Noor, verse number 19)
Islam teaches chastity, modesty and lofty qualities. All the men of understanding know the fact that immodesty, indecency and nudeness destroys the whole society. The progress and development of a society is only through virtuousness, modesty and chastity. For this reason the Holy Quran instructs everybody not even to approach any kind of immodesty be it spoken or otherwise. It orders to avoid indecent songs, pornographic literature. It is extremely necessary for each one of us to avoid character-destroying literature, visual nudity, indecent actions and immodest talk and thoughts in our public and personal lives and in every sleeping and waking moment of our life.
Not only Islam, but also any educated, cultured person will not accept the flood of immodesty and indecency that is flung in our societies on the occasion of Valentine’s Day. It is because of such condemnable acts that fatal diseases like AIDS etc. are inflicted on us. The Holy Prophet (Sallallahu alaihi wa sallam) said:
Translation: 'The nation (group of people) which openly indulges in immodesty will be affected by contagious diseases like plague and other diseases which the earlier people were even aware of.'
The propagation of immodesty mentioned in this verse includes every form of propagation-immodesty in print form i.e. books, etc. immodesty in visual form i.e. images, CDs etc. and every other conceivable form of propagation.
It is in fact a habit of Satan to invite people towards immodesty. As given in Surah Noor-21. Satan makes immodesty seem tempting to the people. They think that happiness and solace is to be found only in this. But they are not aware that Satan is only spreading its net to ensnare them. Those people could not understand the deception of Satan.
The way the whole society draws benefit from people who have virtuousness and lofty character, in the same way the whole society is hurt when immodesty rules the roost and the garment of chastity are rent. It takes a great deal of time and instruction to remove these effects.