Valentine's Day is a holiday celebrated on February 14. It is the traditional day on which lovers express their love for each other; sending Valentine's cards, or offering candy. It is very common to present flowers on Valentine's Day. The holiday is named after two among the numerous Early Christian martyrs named Valentine. The day became associated with romantic love in the circle of Geoffrey Chaucer in High Middle Ages, when the tradition of country love flourished.
Ceremony of Valentine’s Day comes from West (America and Europe). This day becomes popular because of respect to Christian martyrs named Valentine. It is western custom. Because of western custom, it is not appropriate to Indonesia culture also called East custom. Furthermore Islam is the majority religion professed by most native of Indonesia. Ceremony of Valentine’s Day becomes a contasting thing to Islam.
Many ways done by Indonesian teenagers to express love to their boyfriend or girlfriend on Valentine’s Day. Unsual gifts are given and even almost waste money. To celebrate this day, Indonesian teenagers also have behavior like teenagers in West. They perform western habit in their performance and deeds; giving gift by holding hand, kissing and embracing their boyfriend or girlfriend. Indonesian Moslem teenagers also do the same thing when celebrating Valentine’s Day. Indonesian Moslem teenagers are influenced by western custom. Therefore the celebration of Valentine’s Day for Indonesian teenagers generally, and Indonesian Moslem teenagers specially, is not an unsual thing.
Valentine’s Day is a part of Christian (Nasrani) rituals. It is not only related to mere custom but also related to religion istruction (aqidah). Following other religion instruction is the same thing with believing the religion. Islam forbids its follower to follow other religion instruction.
Ceremony of Valentine’s Day currently exchanges in its spirit. In Rome ages, this ceremony is close related to gods and goddesses and mislead myth. In Christian ages, this ceremony is a part of religion holiday symbol. Now, ceremony of Valentine’s Day is identically to a free social intercourse for teenagers. It can be observed by so many feast, dating, giving gift to each other, and even having a sexual act outside of marriage. All deeds above are on the name of love.
Because of spirit of celebrating Valentine’s Day, there is a belief that doing bad sin (maksiat) and some other religion prohibiton like dating, holding hand, embracing, kissing, and having a sexual act outside of marriage are allowed. Moreover, many parents allow their child to celebrate Valentine’s Day. The reason of all deeds above are love, not a sexual desire.
Allah SWT reveals in Alqur’an : Al-Isra’ [17:32] You shall not commit adultery; it is a gross sin, and an evil behavior. And Al-Isra’ [17:36] You shall not accept any information, unless you verify it for yourself. I have given you the hearing, the eyesight, and the brain, and you are responsible for using them. 
Giving a comment of the two verse above, in Islam, the word “tahu” (know) has the meaning as a capable of sensing with all of sense organs controlled by heart. It means that “tahu” is the stage of acquiring knowledge till getting the meaning and essence (real meaning) of an object. “Tahu” is not only have the meaning of knowing the history of an event, seeing or listening, but also have a capacity to know more of a written meaning. Therefore, Islam forbids the belief that comes from the outside of Islamic instruction.
There is a popular hadith has the meaning that who follow the other (religion instruction) he shall be the same with the other. man tasyabbaha bi qaumin fa huwa minhum. This statement gives a clear guidance for us that following anything which comes from the other is a forbidden thing (religion instruction outside of Islam).In conclusion, Islam forbids to celebrate Valentine’s Day in order to purify the faith of its follower. Valentine’s Day is a part of Christian ritual instruction. As the guidance of Alqur’an and hadith said that following any other religion instruction outside of Islam is a bad sin and the doer is a part of the religion he/she follows.