woods-

All religions believe in heaven and hell and all religions have different views whether or not suicide is a sin. In Catholic - it is. In Islam - it isn't (Jihad).

So... the question really... why are you thinking whether or not suicide is a sin? Are you feeling suicidal or making suicide plans?

If you are feeling suicidal due to clinical depression - please seek help immediately. You can call friends or visit a voluntary H. You know that suicidal thoughts in clinical depression is biological and its symptom is temporary.

If you are feeling suicidal to other reasons (adjustment issues, personality issues, etc) - then get some psychotherapy. Or talk therapy with friends/family that you trust. Someone who won't judge you for these thoughts and is able to give you an objectional perspective.