Islam also has classified Seven
sins as "Major." Not all seven are "Deadly" in
this life, as only one (
murder) would have a death penalty. However, anyone who commits one of the Seven Major sins will be punished, possibly on earth but definately in the Hereafter, unless there is true repentance. All of the actions comprising these sins have been forbidden by
God according to the
Quran and by
Muhammad in the
Sunnah.
The Quran says "If you avoid the major sins which you have been forbidden, We will cancel out for you your (other) evil deeds and admit you (to Paradise) with a noble entry."(4:31) Therefore, God has guaranteed Paradise to all of those who avoid the major sins. It is very important for a Believer to avoid these types of sins, since they carry a lot of punishment. Muhammad once said "The five (daily) prayers, Friday to Friday, and Ramadan to Ramadan make atonement for what has happenned since the previous one when major sins have been avoided."
In a hadith, Muhammad(pbuh) says, "Avoid the seven noxious things", and after saying this, he mentions them, "associating any partners with God, practicing magic, killing a person without a just reason, consuming the property of an orphan, devouring usury, fleeing from battle when the army is advancing and slandering chaste women." (quoted in both Sahih Bukhari and Sahih Muslim)
There is some difference of opinion among scholars in this regard. Some say the number of major sins is seven, based on that hadith. Abdullah ibn 'Abbas said: "Seventy is closer to their number than seven," as that hadith does not limit the major sins to those mentioned in it. Rather, it points to the type of sins which fall into the category of "major." That includes crimes that have stated punishments under Islamic law, such as theft, fornication, adultery, and murder. It also includes sins that the Qur'an warns against (as they can be hellworthy), and bad deeds that Muhammad(pbuh) cursed.
Of course, sins have various degrees, since some are more serious than others. There are many other major sins like gambling, stealing, adultery, and suicide, but Muhammad(pbuh) singled out those that everyone must watch out for constantly. There are seventy major sins and many minor ones, but these were specifically emphasized by Muhammad and the prophets before him.
The Seven Major sins of Islam are:
References:
http://www.iqra.net/students/competition/essaysen7.html
http://www.themodernreligion.com/misc/hh/major_sins.htm
http://www.islamic-paths.org/Home/English/Discover/Truths/70Major_Sins.htm