Why is suicide a sin in Islam?
I only know of 34/29 in Qur'an-- rather advising you not to do so than forbidding it.
And they say, "When is this promise, if you should be truthful?" Say, "For you is the appointment of a Day [when] you will not remain thereafter an hour, nor will you precede [it]." -- Qur'an 34:29-30
Hurting others is a sin, and a great one to my knowledge. There are many good people who killed themselves rather than living a disgraceful life. Some of them did so just because they didn't have the "skills" to step on others.
The only thing i can think of is that suicide is rejecting God's word that He doesn't give you a heavier load than you can carry, and that everything is a test, improves your soul to a higher level.
Why is suicide a sin in Islam?
Where in Qur'an said so?
Note: I'm nowhere near talking about suicide bombing or any other political aspects of it.