Once Saved Always Saved is not scriptural. The apostle Paul warns Timothy about the dangers of making a shipwreck of his faith. (I Timothy 1:18-19)
Hebrews 3:12-14 Christians are warned about the dangers of departing from the living God.
Hebrews 12:25 warns about turning away from the one who speaks from heaven!
II Peter 3:17 warns us about the dangers of being led away with the error of the wicked.
Heb 10:38 tells us "if any man draw back, my soul shall have no pleasure in him."
Pro 14:14 The backslider in heart will be filled with the fruit of his ways, and a good man will be filled with the fruit of his ways.
Jer 14:7 "our backslidings are many; we have sinned against you.
Hos 11:7 My people are bent on turning away from me, and though they call out to the Most High, he shall not raise them up at all.
Luk 9:62 Jesus said to him: No man putting his hand to the plough and looking back is fit for the kingdom of God.
Heb 10:38 but my righteous one shall live by faith, and if he shrinks back, my soul has no pleasure in him."
1Ti 4:1 Now the Spirit expressly says that in later times some will depart from the faith by devoting themselves to deceitful spirits and teachings of demons,
2Ti 4:3 For the time is coming when people will not endure sound teaching, but having itching ears they will accumulate for themselves teachers to suit their own passions, and will turn away from listening to the truth and wander off into myths.
Heb 3:12 Take care, brothers, lest there be in any of you an evil, unbelieving heart, leading you to fall away from the living God.
2Pe 3:17 And so, dear friends, since you already know these things, continually be on your guard not to be carried away by the deception of lawless people. Otherwise, you may fall from your secure position.
Hebrews 6:4 “It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the word of God and the powers of the coming age, if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting him to public disgrace.”
There are many more but these people are so not Bible based, that they shrug their shoulders, turn away, say it cannot happen and deny it all.