1 Corinthians 9:2
"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."
Cross References (ranked by relevance)
2 Corinthians 12:12
Truly the signs of an apostle were wrought among you in all patience, in signs, and wonders, and mighty deeds.
John 6:27
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.