Soul sleeping is a heretic doctrine which is the result of Bible verse misinterpretations.
"But as touching the resurrection of the dead, have ye not read that which was spoken unto you by God, saying, I am the God of Abraham, and the God of Isaac, and the God of Jacob? God is not the God of the dead, but of the living.
And when the multitude heard this, they were astonished at his doctrine." (Matthew 22:31-33)
Here, the Lord teaches that Abraham, Isaac, and Jacob are alive, though they have died in the flesh.
As they once lived in the flesh, so they now live in the spirit, though incorruptible and expecting the Lord's glorious return. Likewise, we pray in Christ that those who have been glorified by God in the Holy Spirit may pray with us and for us before God.