Without doubt, brother, the biggest sin in Islam is Shirk. Literally, "association;" in Islam, the association of any visible or finite thing with God or to place any thing, concept or entity above God. Thus, to commit "shirk" is to commit idolatry. Compare the English sense of this term when it is said that one "shirks" one's responsibility.
EDIT: Or so I thought
"I spent thirty years learning manners, and I spent twenty years learning knowledge."
1. Murder (suicide being a form of it) 2.Zina (sex outside of marriage) 3.Shirk (idolatry, associating other things with God, denying God's absolute oneness, paganism or polytheism)
You have a point, though, about apostasy: it could be counted as a fourth, since according to the Koran anyone who knows Islam in their heart and believes, then turns away from the religion and dies disbelieving will be damned.
Imagine! I was on the road to hell when I first came to this board about two years ago. Ron and Aziz saved my soul (along with the grace of God) by re-converting me. It's a shame they won't accept any repayment for it: I owe them anything and everything.
First shirk. Not the wahabi shirk but the real one.
Second, kufr or denying the truth that you feel regarding God
Fifth miserliness even to ones self
Abusing and betraying parents
I went to a lecture last night and the speaker talked a little on this.......
I think the biggest sin is Islam is actualy to not belief in the excistance of Allah.......Anybody agree? but i Agree that if otherwise it would probally be giving Allah a partner therfore trying to lower his status.....But i think to deny his excitance would be far worse than to lower his stature what do you guys think?
Shirk is one of the worst and major sins. But also the two other major sins are Zina and masturbation. Now the punishment for Zina is 100 lashes. That's if the person is not married. But if he/she is married they should be stoned to death. As the Hadith of Rasulullah (Sallallaahu Alayhi Wasallam) says,
‘Allah curses the person who commits masturbation.’
But we must remember that some major sins are at different level. Meaning that there are various kinds of punishments for these Major sins.