Lewis is likely thinking of the following passages here.
2 Thessalonians 3:10 (KJV):"For even when we were with you, this we commanded you, that if any would not work, neither should he eat."
1 Thessalonians 4:11-12 (KJV): "And that ye study to be quiet, and to do your own business, and to work with your own hands, as we commanded you; That ye may walk honestly toward them that are without, and that ye may have lack of nothing."
1 Corinthians 3:13-15 (KJV): "Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is. If any man's work abide which he hath built thereupon, he shall receive a reward. If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.