A.T. Robertson Commentary Mark 7:3

"(For the Pharisees, and all the Jews, except they wash their hands diligently, eat not, holding the tradition of the elders;" — Mark 7:3 (ASV)

Diligently (πυγμη). Instrumental case,

with the fist , up to the elbow, rubbing one hand and arm with the other hand clenched. Aleph had πυκνα probably because of the difficulty about πυγμη (kin to Latin pugnus). Schultess considers it a dry wash or rubbing of the hands without water as a ritualistic concession. The middle voice νιψωντα means their own hands. This verb is often used for parts of the body while λουω is used of the whole body (John 13:10). On the tradition of the elders see on Mt 15:2.