“If I be not an apostle unto others, yet doubtless I am to you: for the seal of mine apostleship are ye in the Lord.”
King James Version (KJV)
9:2 Ye are the seal of my apostleship - Who have received not only faith by my mouth, but all the gifts of the Spirit by my hands.
1Co 9:2 For the seal of mine apostleship ye are. The existence of the church at Corinth, founded by his labors, proved that he was their apostle, at least.