Clement of Alexandria, on 1John 5:16

“He that knoweth his brother to sin a sin which is not to death, let him ask, and life shall be given to him, who sinneth not to death. There is a sin unto death: for that I say not that any man ask.”

“John, too, manifestly teaches the differences of sins, in his larger Epistle, in these words: "If any man see his brother sin a sin that is not unto death, he shall ask, and he shall give him life: for these that sin not unto death," he says. For "there is a sin unto death: I do not say that one is to pray for it. All unrighteousness is sin; and there is a sin not unto death."”

Imported from an open dataset — not yet checked against the printed edition.