Philemon 1:21

Having confidence in thine obedience, knowing that thou wilt do even beyond what I say.

Here is the passage where it is thought Paul had in mind the manumission of Onesimus, and indeed it may well be true. Barry commented thus:

This can hardly refer to anything except the manumission of Onesimus, and possibly his being sent back again to Paul. Exactly in this way Christianity was to work out the release of the slave - not by command, but by free and natural inference of its emphatic declaration of the true brotherhood in Christ.[37]