Yes, Once saved always saved is the correct doctrine and God even triples it three times to prove His point.
- John 10:28. Jesus Christ God, the son says that once He gives life, it’s eternal not temporary or conditional under some sin and no one can pluck them out of His hand.
- John 10:29 shows that the Father also does the same as well.
- Ephesians 1:13-14 shows that God, the Holy Spirit also seals the person, all the way till they go to glory.
- Romans 8:33-35 is definite proof that no matter who condemns you for your sin, God still justifies and nothing can separate you from that.
- Romans 8:38-39 further proves the point that whatever you do in the future, or in present or whoever condemns you, nothing can separate from you being in Christ.
For more information, please check out this article on debunking Lordship salvation.