John 8:56-59

[56]Your father Abraham rejoiced to see My day, and he saw it and was glad.”

[57]Then the Jews said to Him, “You are not yet fifty years old, and have You seen Abraham?”

[58]Jesus said to them, “Most assuredly, I say to you, before Abraham was, I AM.”

[59]Then they took up stones to throw at Him; but Jesus hid Himself and went out of the temple, going through the midst of them, and so passed by.

Jesus said Abraham saw HIm; but when was that?

Answer is in Genesis 18

The Lord with two angels appeared to Abraham.

Genesis 18:1-3,13-14,16-19,22,33

[1]Then[b] the Lord appeared to him[/b] by the terebinth trees of Mamre, as he was sitting in the tent door in the heat of the day.
[2]So he lifted his eyes and looked, and behold, three men were standing by him; and when he saw them, he ran from the tent door to meet them, and bowed himself to the ground,
[3]and said, “My Lord, if I have now found favor in Your sight, do not pass on by Your servant.
[13]And the Lord said to Abraham, “Why did Sarah laugh, saying, ‘Shall I surely bear a child, since I am old?’
[14]Is anything too hard for the Lord? At the appointed time I will return to you, according to the time of life, and Sarah shall have a son.”
[16]Then the men rose from there and looked toward Sodom, and Abraham went with them to send them on the way.
[17]And the Lord said, “Shall I hide from Abraham what I am doing,
[18]since Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him?
[19]For I have known him, in order that he may command his children and his household after him, that they keep the way of the Lord, to do righteousness and justice, that the Lord may bring to Abraham what He has spoken to him.”
[22]Then the men turned away from there and went toward Sodom, but Abraham still stood before the Lord.

[33]So the Lord went His way as soon as He had finished speaking with Abraham; and Abraham returned to his place.