Alma 39:6

for behold, if ye deny the Holy Ghost when it once hath had place in you, and ye know that ye deny it; behold, this is a sin which is unpardonable; yea, and whosoever murdereth against the light and knowledge of God, it is not easy for him to obtain forgiveness; yea, I say unto you, my son, that it is not easy for him to obtain a forgiveness.

If you reject the Holy Spirit after it has been with you, and you know that you are rejecting it, this is a sin that cannot be forgiven. And whoever kills when they know God’s truth will have a hard time getting forgiveness. I say to you, my son, that it is not easy to get forgiveness for that.

If you deny the Holy Spirit after he’s dwelt in you, and you know full well what you’re doing—that’s an unforgivable sin. And when someone murders with full knowledge of God’s light, forgiveness doesn’t come easy. I’m telling you, it’s not easy to obtain forgiveness for that.