Caman77555: The Quran Denies that God had a Son. 

RKC: The Qur’an denies God has a son in the literal sense, but not figuaratively. Figuaratively, Judaism records many people as being sons of The Father.

Surah 21

26. And they say: "((Allah)) Most Gracious has begotten offspring." Glory to Him! they are (but) servants raised to honour.

Caman77555: It accepts the theory  that Jesus was a Prophet.

RKC: So does the Bible. The Qur’an, also, says he is the Messiah.

Matthew 21

¹⁰ And when he entered Jerusalem, all the city was stirred, saying, "Who is this?"

¹¹ And the crowds said, "This is the prophet Jesus from Nazareth of Galilee."

Surah 5:72-76
72. They do blaspheme who say: "Allah is Christ the son of Mary." But said Christ: "O Children of Israel! worship Allah, my Lord and your Lord." Whoever joins other gods with Allah,- Allah will forbid him the garden, and the Fire will be his abode. There will for the wrong-doers be no one to help.
73. They do blaspheme who say: Allah is one of three in a Trinity: for there is no god except One Allah. If they desist not from their word (of blasphemy), verily a grievous penalty will befall the blasphemers among them.
74.  Why turn they not to Allah, and seek His forgiveness? For Allah is Oft-forgiving, Most Merciful.
75. Christ the son of Mary was no more than a messenger; many were the messengers that passed away before him. His mother was a woman of truth. They had both to eat their (daily) food. See how Allah doth make His signs clear to them; yet see in what ways they are deluded away from the truth!
76. Say: "Will ye worship, besides Allah, something which hath no power either to harm or benefit you? But Allah,- He it is that heareth and knoweth all things."

Caman77555: I do not know why they believe a Lying Prophet who claims to be the Son of God?

RKC: Muhammad never claimed to be “the Son of God”.