Mark 7:5

Then the Pharisees and scribes asked him, Why walk not thy disciples according to the tradition of the elders, but eat bread with unwashen hands?

Cross-reference

Mark 2:16-18 shows a similar challenge: Pharisees question Jesus' disciples about eating and fasting, another tradition dispute.

Matthew 15:2 records the same question from Pharisees about hand-washing, a direct parallel account.