Why do you think there would be such a silly verse? Because Scripture NEVER describes one who has believed, but then ceases to believe, an unbeliever. That occurs only in your mind, but not the Bible.
So you can cease from asking this irrelevant and silly question.
I have shown that God's gifts are irrevocable, from Rom 11:29. And that eternal life is one of God's gifts, from Rom 6:23. Connecting those dots just isn't that difficult. You won't connect them because you are convinced that one can lose eternal life, but that is in spite of what the Scripture very clearly states.
One who has believed has the irrevocable gift of eternal life. So even if such a one ceases to believe, he still possesses the irrevocable gift of eternal life.
You've failed to prove otherwise from Scripture.
Yes, it's in my mind, and it got there by reading it in the bible.
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. Luke 8:13
Those who believe for a while, then no longer believe, have become un-believers.
Believe = Saved
Believe for a while = Saved for a while
JLB