Prohibitions in Islam

• Allah is the All Wise. He never prohibits something unless it is harmful to man.
• The Muslim's true faith and love for Allah is reflected in his refrainment  from what Allah has forbidden, even if such refrainment confronts one's own wishes and desires. The Muslim must always seek to please  Allah and give precedence to what pleases Allah over what pleases him/herself.

SOME OF THE MAJOR SINS IN ISLAM ARE AS FOLLOWS:

1. Shirk (polytheism) as mentioned in this previous blog.
2. Ridiculing Islam, or hating it.
3. Dissatisfaction with Allah's decree or cursing of time (because of misfortune, calamity, or failure to succeed).
4. Making lawful that which Allah has made unlawful or vice versa. To speak about what you do not know about Islam.
5. Innovating in Islam (e.g. saying one's intention aloud, celebrating the birth of the Prophet, celebrating the night of mid-Sha'baan, the night of Al-Isra wal Mi'raj, and the night of Al-Qadr in Ramadan... etc.)
6. Cursing or insulting  any of the Prophet's companions.
7. Fortunetelling, magicism and similar things to these.
8. Not observing prayer in its prescribed time and, for men, not offering it in the Masjid in congregation.
9. Not giving out the obligatory Zakah.
10. Not fasting in Ramadan without an Islamic exception.
11. Suicide and murder.
12. Fleeing from enemies in the battle.
13. Fornication, sodomy, and masturbation.
14. Falsely accusing others of fornication.
15. Consuming the orphan's wealth and exercising injustice against him.
16. Riba or usury (e.g. to loan someone 100$ for 110$ on credit).
17. Bribery.
18. Gambling.
19. Theft, damaging entrusted property, not paying debts, and any unlawful way of acquiring wealth.
20. Extravagance, misuse and squandering of wealth.
21. Showing disrespect towards parents.
22. Harming or offending relatives.
23. Harming or offending neighbors and the public.
24. Vandalizing (i.e. destroying or damaging public places and facilities).
25. Oppressing others, exercising injustice against them and abetting the oppressor against the oppressed.
26. Torturing animals.
27. Perjury and concealment of truth.
28. Telling lies, breaking promises, and forgery.
29. Treachery, disloyalty, and disclosing secrets.
30. Envy.
31. Arrogance and ridiculing others.
32. Backbiting and slandering.
33. Music.
34. Alcohol and drugs.
35. Eating the meat of dead animals, blood, or any other unlawful food.
36. Eating pork, dog meat, predatorial animals (animals that humt other animals), and birds of prey.
37. Eating an animal slaughtered in the name of other than Allah.
38. Keeping a dog without a legitimate Islamic excuse for doing so.
39. Wearing, hanging, or using the Christian cross and any other symbols which contradict Islam.
40. Wearing gold and silk and wearing garments which fall below ankle level (for men). However, it is permissible for women to wear gold and silk. They should also wear their garments below ankle-level.

It is worth emphasizing that Islam considers all dealings, acts, and transactions as lawful as long as there aren't any evidences that prove their illegality. Hence, Islam specifies what's forbidden and when it abstains from passing a ruling about something it is regarded as lawful.