1 Corinthians 15:14, 58
1 Corinthians 15:14 NASB1995
and if Christ has not been raised, then our preaching is vain, your faith also is vain.
1 Corinthians 15:58 NASB1995
Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your toil is not in vain in the Lord.