1 John 5:16 NKJV
If anyone sees his brother sinning a sin which does not lead to death, he will ask, and He will give him life for those who commit sin not leading to death. There is a sin leading to death. I do not say that he should pray about that.
God is so merciful that He allows us to be vessels of intercession for our brothers and sisters who have sinned. We can stand in the gap and help someone who has fallen avoid death or destruction. We need to take that seriously. God wants us to have a heart of compassion like His. He is not looking for opportunities to condemn. He looks for opportunities to save. John mentions in this verse a category of sin that leads to death that we are not allowed to pray about. It does not necessarily mean the person is going to Hell. It could just mean their life on earth will be cut short. There are rare occasions when God has closed the door on someone and we can no longer intercede for them. We can find examples in the Bible. If we are sensitive to the Holy Spirit, He will let us know when we are dealing with a case like that. I have had a few occasions when I have encountered a such situations. However, unless it is clear that God has closed the door, we should pray for deliverance for those who have sinned.