Jesus visits the souls in prison. This verse is often brought up when talking about purgatory/praying for the dead.

This idea of Jesus visiting the souls in prison is probably taken from Peter’s first letter, where it says, For Christ also died for sins once for all, the righteous for the unrighteous, to bring you to God. He was put to death in the body but made alive in the Spirit, through whom also he went and preached to the spirits in prison who disobeyed long ago when God waited patiently in the days of Noah while the ark was being built—I Peter 3:18-20a. In the context of this section of First Peter, it actually is probably referring to a pre-incarnate Christ preaching through the words of Noah to those unbelievers in the days before the Flood. They were imprisoned by their sin, and doomed to eternity apart from God outside of repentance. The fact is, there are no chances for salvation once death has occurred; that’s why Christians need be involved in evangelism while God patiently waits, that those outside the Kingdom may come to saving faith in Jesus Christ. Praying for the dead has existed since ancient Judaism, not to mention showing itself in many other religious traditions. Biblically, there is no foundation for that