If God became a man, we would expect Him to be without Sin

1. Jesus’s View of Himself
To a hostile crowd:
“Which of you convicts Me of sin?” John 8:46
He got no answer. Though He invited scrutiny, no one could accuse him of anything. He was innocent. He could encourage this public examination because He was without sin.
John 8:29: “I always do those things that please Him.”
He was in unbroken communion with His Father in heaven.
Another quality which has often been remarked was the absence of any sense of having committed sin or of a basic corruption of Himself. It is highly significant that in one as sensitive morally as was Jesus and who taught His followers to ask for the forgiveness of their sins there is no hint of any need for forgiveness for Himself, no asking of pardon, either from those about Him or of God.
Kenneth Scott Latourette, Historian, A History or Christianity, 47
The best reason to consider Him sinless: “is the fact that He allowed His dearest friends to think that He was (sinless). There is in all His talk no trace of regret or hint of compunction or suggestion of sorrow for shortcoming, or slightest vestige of remorse. He taught other men to think of themselves as sinners, He asserted plainly that the human heart is evil, He told His disciples that every time they prayed they were to pray to be forgiven, but He never speaks or acts as though He himself has the faintest consciousness of having ever done anything other than what was pleasing to God. Jefferson, CJ, 225
Another quality which has often been remarked was the absence of any sense of having committed sin or of a basic corruption of Himself…It is highly significant that in one as sensitive morally as was Jesus and who taught His followers to ask for the forgiveness of their sins there is no hint of any need for forgiveness for Himself, no asking of pardon, either from those about Him or of God.
Kenneth Scott Latourette, Historian, A History or Christianity, 47
2. The Witness of His Friends
Jesus’ closest associates, Peter and John, attest to His being without sin:
1 Peter 1:19: “but with the precious blood of Christ, as of a lamb without blemish and without spot.”
1 Peter 2:33: “Who committed no sin, nor was guile found in His mouth.”
1 John 3:5: “And you know that He was manifested to take away our sins, and in Him there is no sin.”
While saying this, John also declared that anyone who declares himself to be without sin, he is a liar and he is calling God a liar also!!!
Even Judas—the one responsible for Jesus’ death—recognized Jesus’ innocence. “I have sinned by betraying innocent blood” Mt 27:3,4
Hebrews 4:15: “For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin”
3. The Witness of His Enemies
One thief rebuked the other: This Man has done nothing wrong.” Luke 23:41
Pilate also found Jesus innocent of wrong-doing “You have brought this Man to me, as one who misleads the people. And indeed, having examined Him in your presence, I have found no fault in this Man concerning those things of which you accuse Him” Luke 23:14
The Roman centurion at the cross of Jesus: “Certainly this man was innocent” Luke 23:47