2 Corinthians 12:9:

And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.

See also:

God Uses Real People
Objection: God Wouldn’t Heal Paul’s Thorn in the Flesh
Objection: Paul GLORIED in His INFIRMITIES – the Same Greek Word Used in Matthew 8:17 of What Jesus Took.  If Matthew 8:17 Refers to the Atonement, How Could Paul Glory in What Christ Took Away?