20 Then Matthew's report goes on thus: “Now the chief priests and elders and all the council sought false witness against Jesus, to put Him to death, but found none: yea, though many false witnesses came, yet found they none.” Mark comes in here with the explanation, that “their witness agreed not together.” But, as Matthew continues, “At the last came two false witnesses, and said, This fellow said, I am able to destroy the temple of God, and to build it in three days.” Mark states that there were also others who said, “We have heard him say, I will destroy this temple that is made with hands, and within three days I will build another made without hands.
And therefore (as Mark also observes in the same passage) their witness did not agree together.” Then Matthew gives us the following relation: “And the high priest arose and said unto Him, Do you answer nothing? What is it which these witness against you? But Jesus held His peace. And the high priest answered and said unto Him, I adjure you by the living God, that you tell us whether you be the Christ, the Son of God. Jesus says unto him, You have said.” Mark reports the same passage in different terms, only he omits to mention the fact that the high priest adjured Him.
He makes it plain, however, that the two expressions ascribed to Jesus as the reply to the high priest—namely, “You have said,” and, “I am,” — really amount to the same. For, as the said Mark puts it, the narrative goes on thus: “And Jesus said, I am; and you shall see the Son of man sitting on the right hand of power, and coming with the clouds of heaven.” This is just as Matthew also presents the passage, with the solitary exception that he does not say that Jesus replied in the phrase “I am.”
Again, Matthew goes on further in this strain: “Then the high priest rent his clothes, saying, He has spoken blasphemy; what further need have we of witnesses? Behold, now you have heard his blasphemy. What do you think? And they answered and said, He is guilty of death.” Mark's version of this is entirely to the same effect. So Matthew continues, “Then did they spit in His face, and buffeted Him, and others smote Him with the palms of their hands, saying, Prophesy unto us, you Christ, Who is he that smote you?” Mark reports these things in like manner. He also mentions a further fact, namely, that they covered His face. On these incidents we have likewise the testimony of Luke.
Source: The Harmony of the Gospels (New Advent)