Before Abraham was, I am.

"Your father Abraham rejoiced to see my day: and he saw it, and was glad.

“Then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham? [Abraham lived approximately 2000 years earlier.] 

“Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I am.

“Then took they up stones to cast at him: but Jesus hid himself, and went out of the temple, going through the midst of them, and so passed by." - John 8:56-59 KJV

Why did the Jews take up stones to cast at Jesus?

Because they understood that Jesus was letting them know He is God, the “I AM.”

"And God said unto Moses, I AM THAT I AM: and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you." - Exodus 3:14 KJV