1 Corinthians 15:2, 58
1 Corinthians 15:2 NASB1995
by which also you are saved, if you hold fast the word which I preached to you, unless you believed in 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.