1 John 5:16 in the King James Version
If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
Context
15 And if we know that he listens to us, whatever we ask, we know that we have the petitions which we have asked of him.
16 If anyone sees his brother sinning a sin not leading to death, he shall ask, and God will give him life for those who sin not leading to death. There is sin leading to death. I don’t say that he should make a request concerning this.
17 All unrighteousness is sin, and there is sin not leading to death.