But some of the Pharisees asked, “Why are you doing what is unlawful on the Sabbath?”
These two passages of story we had both in Matthew and Mark, and they were there laid together (Mat 12:1; Mar 2:23; Mar 3:1), because, though happening at some distance of time from each other, both were designed to rectify the mistakes of the scribes and Pharisees concerning the sabbath day, on the bodily rest of which they laid greater stress and required greater strictness than the Law-giver intended.
Commenting on Luke 6:1-11
And certain of the Pharisees said unto them,.... Unto the disciples. The Evangelists Matthew and Mark say, that they said this to Jesus: no doubt but they said it to both, first to one, and then to the other; probably last of all to Christ, who returned an answer to it: why do ye that which is not lawful on the sabbath day?
Verse 2. No entry from BARNES for this verse. (b) "that which is not lawful"