Is it ever right to pray for the death of a believer who is sinning?
No, it is never right to pray for the death of a believer caught in sin. Scripture teaches there is a sin unto death, but John explicitly says he does not say to pray for it. No believer or church body has the right to pray for an erring believer's death; that remains in God's hands.
Les explains from this passage that Galatians 6:1 calls spiritual believers to restore someone caught in a fall with a spirit of meekness, remembering that everyone is prone to sin. John delineates that some sins do not cause God to take a believer out of physical life, but some do. If a believer refuses to turn from a sinful lifestyle, God may suddenly take them home—through a heart attack or car accident—lest they keep bringing reproach to His name. That is the sin unto death. However, John says, 'I do not say that you shall pray for it.' No believer or church body ever has the right to pray for the death of an erring believer. That is never permissible; it is in God's hands.
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.
More Questions
What is the sin unto death that John says not to pray for?
According to John's epistle there is a sin unto death, and John warns that you should not pray for it.
Do believers who commit the sin unto death lose their salvation?
Believers who commit the kind of deep, open sin that God removes from physical existence by death do not lose their salvation—Scripture says God takes them out of their physical existence, but they are still saved.