Some of the circles of friends I am in (mind you most of them are Christians) say that masturbation is not sin. Is there a verse in the bible that says masturbation is a sin?
Well, the first verse that comes to mind is this:
Matthew 5:27-28 New King James Version (NKJV)
Adultery in the Heart
27 “You have heard that it was said to those of old, ‘You shall not commit adultery.’ 28 But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart.
If someone could somehow masturbate without lustful thoughts (perhaps that would be night emissions) then I suppose it could be “not a sin”. But generally speaking, we lust when we masturbate, and lust is “Adultery in the Heart” which Jesus says is the same as plain old adultery, which is a sin in the 10 Commandments. That makes it a sin in the Old Testament and updated by Jesus Christ Himself in the New Testament, meaning it counts for Christians too. So, yes, it is a sin.