It is absurd to ask for proof of the existence of God because it is revealed that Jesus is YHWH God (Matthew 16:13-20, Luke 10:22, John 1:49).

If the atheist (or the believers wo do not understand the Godhead) who includes in his rant the inexistence of the God of Abraham, Isaac, Jacob, Moses, the Jews, and all humankind could come to understand the concept of Jesus (God) from the Jews, the person must deny that Jesus ever existed (an aberration) in order to reject the existence of God because Jesus in flesh is the same YHWH God in Heaven.

Matthew 16:20 ASV
(20)  Then charged he the disciples that they should tell no man that he was the Christ.

Luke 10:22 ASV
(22)  All things have been delivered unto me of my Father: and no one knoweth who the Son is, save the Father; and who the Father is, save the Son, and he to whomsoever the Son willeth to reveal him.

John 1:49 ASV
(49)  Nathanael answered him, Rabbi, thou art the Son of God; thou art King of Israel.

Zephaniah 3:15 ASV
(15)  Jehovah hath taken away thy judgments, he hath cast out thine enemy: the King of Israel, even Jehovah, is in the midst of thee; thou shalt not fear evil any more.