O yes, I’m afraid “once saved, always saved” does not come from the Bible. Here are a selection of passages that talk about “falling away”, “departing from the faith”, “turning back” and being “drawn away”.

Hebrews 10     ²⁶ For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, ²⁷ but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries. ²⁸ Anyone who has rejected Moses’ law dies without mercy on the testimony of two or three witnesses. ²⁹ Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace?

Luke 8:13    But the ones on the rock are those who, when they hear, receive the word with joy; and these have no root, who believe for a while and in time of temptation fall away.

Hebrews 6     ⁴ For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, ⁵ and have tasted the good word of God and the powers of the age to come, ⁶ if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.

Ezekiel 33:18    When the righteous turns from his righteousness and commits iniquity, he shall die because of it.

1 Timothy 4      Now the Spirit expressly says that in latter times some will depart from the faith, giving heed to deceiving spirits and doctrines of demons, ² speaking lies in hypocrisy, having their own conscience seared with a hot iron,

2 Peter 2     ²⁰ For if, after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning. ²¹ For it would have been better for them not to have known the way of righteousness, than having known it, to turn from the holy commandment delivered to them.

1 Samuel 10     ⁶ Then the Spirit of the LORD will come upon you, and you will prophesy with them and be turned into another man.

⁹ So it was, when he had turned his back to go from Samuel, that God gave him another heart; and all those signs came to pass that day. ¹⁰ When they came there to the hill, there was a group of prophets to meet him; then the Spirit of God came upon him, and he prophesied among them.

1 Samuel 15     ¹⁰ Now the word of the LORD came to Samuel, saying, ¹¹ “I greatly regret that I have set up Saul as king, for he has turned back from following Me, and has not performed My commandments.”

Acts 20     ²⁸ Therefore take heed to yourselves and to all the flock, among which the Holy Spirit has made you overseers, to shepherd the church of God which He purchased with His own blood. ²⁹ For I know this, that after my departure savage wolves will come in among you, not sparing the flock. ³⁰ Also from among yourselves men will rise up, speaking perverse things, to draw away the disciples after themselves.

2 Peter 2      ¹ But there were also false prophets among the people, even as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Lord who bought them, and bring on themselves swift destruction.

² And many will follow their destructive ways, because of whom the way of truth will be blasphemed. ³ By covetousness they will exploit you with deceptive words; for a long time their judgment has not been idle, and their destruction does not slumber.

I hope this answers your question. Of course, if we stay in a close relationship with God, we can avoid the devil’s snares to pull us away from God.  God bless!