John Chrysostom

But it were meet first to inquire, why the disciples ate with unwashen hands. Wherefore then did they so eat? Not as making a point of it, but as overlooking henceforth the things that are superfluous, and attending to such as are necessary; having no law to wash or not to wash, but doing either as it happened. For they that despised even their own necessary food, how were they to hold these things worth much consideration? …

Homily on the Gospel of Matthew 51 ↗

Bede

Taking carnally those words of the Prophets, in which it is said, Wash, and he ye clean, they, observed it only in washing the body; (Is. 1:16.) hence they had laid it down that we ought not to eat with unwashen hands.

Catena Aurea by Aquinas ↗

Thomas Aquinas

Then is presented that in which they accused them: why do your disciples transgress the traditions of the ancients? It was commanded, as is found in Deut. 4:2: you shall not add to the word that I speak to you, neither shall you take away from it. Hence by adding traditions, they were acting against the law; not that it was unlawful to establish something, but that they commanded their traditions to be observed just as the law of the Lord. For they do not wash their hands etc. Here is explained what their traditions are. …

Commentary on Matthew ↗

Remigius of Rheims

Of what kind these traditions were, Mark shows when he says, The Pharisees and all the Jews, except they wash their hands oft, eat not. (Mark 7:3.) Here then also they find fault with the disciples, saying, For they wash not their hands when they eat bread. Or the Pharisees found fault with the Lord's disciples, not concerning that washing which we do from ordinary habit, and of necessity, but of that superfluous washing which was invented by the tradition of the elders.

Catena Aurea by Aquinas ↗