Jesus claimed to have existed even before Abraham.
(John 8:57-59 NIV) “You are not yet fifty years old,” the Jews said to him, “and you have seen Abraham!” {58} “I tell you the truth,” Jesus answered, “before Abraham was born, I am!” {59} At this, they picked up stones to stone him, but Jesus hid himself, slipping away from the temple grounds.
Jesus asserted His divinity by the use of the present tense “I am”. If He had only wanted to say He had existed before Abraham, He would have used “I was”.
Upon hearing this, the Jews picked up stones to stone him because they equated this to blasphemy. They understood Jesus was claiming to be the forever existent God.
Muslim response: Jesus only existed in God’s foreknowledge, like the prophet Jeremiah.
Jeremiah 1:5 “Before I (God) formed you in the womb, I knew you before you were born I set you apart; I appointed you as a prophet to the nation.”
Christian reply
Muslims are right in saying that the above verse shows that Jeremiah existed in God’s foreknowledge only. The words “before I formed you” tells us that Jeremiah had not actually existed yet. But Jn 8:58 could not have been referring to Jesus existing in the foreknowledge of God since God, who is all knowing, would also have foreknown Abraham. How could God who is all-knowing have foreknown Jesus before he foreknew Abraham, never mind who was born first. (It is even more unlikely since Abraham was born first.) Therefore Jn 8:58 could only mean that Jesus pre-existed with God.
When Jesus claimed to be eternally existent with God, it is a claim to deity. If one is not God, how can one be eternally existent with God?
Jesus saw the downfall of Satan – something which happened before he was on earth
Jesus said, “I saw Satan fall like lightning from heaven” (Luke 10.18). Muslims believe, following the Quran (Surah 7.8) that Satan was cast down in disgrace right at the beginning of creation. When Jesus said that he saw him fall, it was his way of saying “I was there, I saw it happen” – a telling testimony to his presence in heaven even from the beginning of the world.
Jesus’ claim to have existed eternally with God is also confirmed by the Old Testament
Some people argue that Jesus did not claim to be God and that this idea of an eternally existent being coming to earth is something which Christians invented because they misinterpreted Jesus’ sayings. But not so. We can find such statements even in the Old Testament.
But you, O Bethlehem Ephrathah, who are little to be among the clans of Judah, from you shall come forth for me one who is to be ruler in Israel, whose origin is from of old, from ancient days. Micah 5.2
When one talks about a being from ancient days, he is referring to God himself.
(Isa 43:12-13 NIV) I have revealed and saved and proclaimed– I, and not some foreign god among you. You are my witnesses,” declares the LORD, “that I am God. {13} Yes, and from ancient days I am he. No one can deliver out of my hand. When I act, who can reverse it?”
(Dan 7:9 NIV) “As I looked, “thrones were set in place, and the Ancient of Days took his seat. His clothing was as white as snow; the hair of his head was white like wool. His throne was flaming with fire, and its wheels were all ablaze.