1 Peter 4:1

1 Peter 4:1. Forasmuch then as Christ hath suffered for us in the flesh, arm yourselves likewise with the same mind:

Accepting this great truth, that it is well that the flesh should die that the spirit may triumph, even as it was with Christ.

1 Peter 4:1. For he that bath suffered in the flesh hath ceased from sin;

If he has indeed died with Christ, and the power of Christ’s sufferings has made him dead to sin, he has ceased from it.