Romans 14
5 Ref One man esteems one day as more important. Another esteems every day alike. Let each man be fully assured in his own mind.
6 Ref He who observes the day, observes it to the Lord; and he who does not observe the day, to the Lord he does not observe it. He who eats, eats to the Lord, for he gives God thanks. He who doesn't eat, to the Lord he doesn't eat, and gives God thanks.