2 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.
1 Corinthians 9:2 Cross References - KJV_Cambridge
John 6:27
27 Labour not for the meat which perisheth, but for that meat which endureth unto everlasting life, which the Son of man shall give unto you: for him hath God the Father sealed.
2 Corinthians 3:1-3
1 Do we begin again to commend ourselves? or need we, as some others, epistles of commendation to you, or letters of commendation from you?
2 Ye are our epistle written in our hearts, known and read of all men:
3 Forasmuch as ye are manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart.
2 Corinthians 12:12
12 Truly the signs of an apostle were wrought among you in all patience, in signs, and wonders, and mighty deeds.