Found in Matthew 15:1-20 and Mark 7:1-23
Twice Jesus was questioned about unwashed hands.
The first time was in Luke 11:37-54. After Jesus was accused of casting out devils by the prince of devils, Beelzebub, a Pharisee asked Jesus to dine with him: and Jesus went in, and sat down to meat.
The Pharisee saw this and marveled that Jesus had not first washed before dinner. Jesus said, The Pharisees make the outside of the cup and the platter clean; but your inward part is full of ravening and wickedness. Didn’t he that made that which is outside make that which is inside also? Give alms of such things as you have; and, behold, all things are clean unto you. (Vs 37-41)
Jesus went on to reproach the Pharisees and the lawyers also.
And the scribes and the Pharisees began to urge Jesus vehemently, and to provoke him to speak of many things: Laying wait for him, and seeking to catch something out of his mouth, that they might accuse him. (Vs 53-54)
Unwashed Hands Questioned Again
After Jesus spoke about the Bread of Life, many of his followers left him. (John 6:56)
Then the Pharisees, and certain of the scribes came to Jesus from Jerusalem. They saw that some of his disciples ate bread with unwashed/defiled hands, and they found fault. (Mark 7:1-2)
In vs 3-4, Mark explains why this was offensive to the scribes and Pharisees. The Pharisees, and all the Jews, held the tradition of the elders; they would not eat unless they washed their hands. And when they came from the market, except they wash, they would not eat. And they held many other traditions, such as the washing of cups, and pots, brasen vessels, and of tables. (Brasen vessels were those made of brass, bronze and copper.)
Pharisees and scribes: Why do your disciples not walk according to the tradition of the elders, but eat bread with unwashed hands?
Jesus: Isaiah has prophesied well of you hypocrites. This people honors me with their lips, but their heart is far from me. Howbeit in vain do they worship me, teaching for doctrines the commandments of men. (Isaiah 29:13) You reject the commandment of God, that you may keep your own tradition.
There is nothing from outside a man, that entering into him can defile him: but the things which come out of him, those are they that defile the man. (Mark 7:15)
Matthew 15:17-20 Whatever enters in at the mouth goes into the belly, and is cast out into the draught. But those things which proceed out of the mouth come forth from the heart; and they defile the man. For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies (covetousness, wickedness, deceit, lasciviousness, an evil eye, pride, foolishness: All these evil things come from within – Mark 7:22-23): These are the things which defile a man: but to eat with unwashed hands does not defile a man.
It is in Matthew 15:14 that Jesus says of the Pharisees: They are blind leaders of the blind. And if the blind lead the blind, both shall fall into the ditch. (Also found in Luke 6:39 as a general truth)