Commentaries:
This ties in with Galatians 1:14, where Paul writes about being "zealous for the traditions of my fathers"—his description of the national religion of Judaism. Jesus' disciples transgressed the tradition of the elders, not the law of God. One cannot find a command concerning what they are accused of in God's law.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Twenty-Four)