2 Peter 2:20-22

Now, if, having fled away from the pollutions of the world, through the knowledge of the Lord and Saviour Jesus Christ, and being again entangled, they are overcome by them; their last condition is worse than the first.

1 John 5:16

If any one see his brother sinning a sin, not to death, let him ask, and he will grant to him life, for those who sin not to death. There is a sin leading to death. I do not say concerning it, that you should ask.

Treasury of Scripture Knowledge

Summary

For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,

General references

Bible References

It is

2 Peter 2:20
Now, if, having fled away from the pollutions of the world, through the knowledge of the Lord and Saviour Jesus Christ, and being again entangled, they are overcome by them; their last condition is worse than the first.
1 John 5:16
If any one see his brother sinning a sin, not to death, let him ask, and he will grant to him life, for those who sin not to death. There is a sin leading to death. I do not say concerning it, that you should ask.

General references

Jude 1:22
And making a difference, have compassion, indeed, on some: