These are quotes about soul sleep from throughout Christian history.
I do not say, indeed, that all souls die. That would truly be a piece fo good fortune to evil people. What then? The souls of the godly remain in a better place, while those of the unrighteous and wicked are in a worse place, waiting for the time of judgment. Thus some which have appeared worthy of God never die, but others are punished so long as God will them to exist and be punished. (Dialogue with Trypho, a Jew 5)
[This is Trypho, the Jew, speaking, so it does not necessarily represent Christian thinking.] The soul partakes of life, since God wills it to live. Thus, then, it will not partake when God does not will it to live. For to live is not its attribute, as it is God's. Instead, as a man does not live always, and the soul is not joined with the body forever, then whenever this harmony must be broken up, the soul leaves the body, and the man exists no longer. Even so, when the soul must cease to exist, the spirit of life is removed from it, and there is no more osul, but it goes back to the place from where it was taken. (Dialogue with Trypho, a Jew 6)