Muhammad's Plagiarism: Stealing Ideas from Forgeries, False Heretical Teachings, and Jewish Fables
Muhammad Borrowed Information from Christian Forgeries, Jewish Fables, and a Mistranslation:
The evidence seems to clearly indicate that Muhammad used and was influenced by late, false gospels and Christian forgeries. These false gospels were written decades, and some even centuries, after the four true canonical Gospels of Matthew, Mark, Luke, and John were written by Jesus' disciples and followers in the 1st century.
Scholar Oddbjørn Leirvik states: "In the Qur'an and in the sound Hadith, there is obvious influence from the non-canonical ('heretical') Christianity prevailing in the Arab peninsula and in Abyssinia." 
Not only does the evidence show that Muhammad used heretical Christian forgeries as sources for his teachings, but he also used Jewish legends and a mistranslation as well.
Below is a list of some of Muhammad's use of heretical false gospels, Christian forgeries, and Jewish legends in his teachings:
Muhammad said Jesus talked from the cradle (Surah 3:46, 5:110 19:28-34), but this is a fable found in The Arabic Infancy Gospel (also known as The First Gospel of the Infancy of Jesus Christ), which is dated to the 5th-6th century.
He said Jesus turned clay birds into real birds (Surah 3:49, 5:110), but this is another fable found in The Infancy Gospel of Thomas, a 2nd century writing.
He said that Jesus was not crucified but that it only appeared that way (Surah 4:157-158), but this historically false belief predates Islam, being found in the false gnostic gospels of The Apocalypse of Peter, a pseudepigraphal work from the 2nd century, and The Second Treatise of the Great Seth, which is dated to around the 2nd-4th century. Both of these works were found in the Nag Hammadi documents in 1945.
He told a story of Mary and the miracle of the palm tree and the stream of water (Surah 19:22-26), but a version of this can be found in chapter 20 of The Gospel of Pseudo-Matthew (also known as The Infancy Gospel of Matthew), which is dated possibly prior to the 6th century (but might be from the 8th or 9th century).
Much of what Muhammad said in the Quran about the selection and upbringing of Mary parallels what is found in the Protovangelium of James, a 2nd century writing also known as The Infancy Gospel of James (e.g. In the Protovangelium of James it says Mary was fed in the temple by an angel, and in the Quran Muhammad said Mary was fed in the temple by Allah in Surah 3:37, etc...).
The saying in Surah 5:32 that "whosoever killeth a human being... it shall be as if he had killed all mankind, and whoso saveth the life of one, it shall be as if he had saved the life of all mankind" (Translation by Pickthall) is not originally from Muhammad but rather it's from Mishnah Sanhedrin 4:5, Yerushalmi Talmud 4:9, and the Babylonian Talmud Sanhedrin 37a.
He said the angels spoke out against the creation of man (Surah 2:30), but this fable is found in the Babylonian Talmud Sanhedrin 38b.
He said the angels didn't know the names of the animals but Adam did (Surah 2:30-33), but this fable is found in Midrash Bereishit Rabbah 17:4-5 and Midrash Tanchuma Chukat 6:1.
He said Satan rebelled against Allah and refused to submit and prostrate before Adam (Surah 7:11-18, 15:28-35, 17:62, 38:71-85), but this story is found in the pseudepigraphal work called Life of Adam and Eve, composed around the 1st century BC or the 1st century AD, and in a 6th century Syriac work called The Cave of Treasure.
He said Cain had to learn to bury the body of his brother Abel from a bird (a raven in the Quran) (Surah 5:31), but this story is found in Midrash Tanchuma Bereshit 10:2.
He presented the story of Abraham smashing idols as an historical fact (Surah 6:74, 21:51-71), but this story is actually a Jewish legend invented by Rabbi Hiyya in the 2nd century and recorded in Midrash Bereishit Rabbah 38:13.
He said Abraham was delivered from a fire (Surah 21:68-70), but this is also a Jewish legend found in Midrash Bereishit Rabbah 38:13 and is based on a mistranslation of Genesis 15:7 by a Jewish rabbi named Jonathan Ben Uzziel who confused the Babylonian word "Ur" which means "city" with the Hebrew word "Ur" which means fire.
He said Korah was extremely wealthy (Surah 28:76), but this is a Jewish legend found in Babylonian Talmud Sanhedrin 110a and Babylonian Talmud Pesachim 119a.
It is reported in the Hadith that Muhammad said Adam was 60 cubits tall, and that people have been decreasing in stature since Adam's creation (Sahih Al-Bukhari 55:543), but this belief of Adam being extremely tall is a Jewish fable found in the Babylonian Talmud Bava Batra 75a and Babylonian Talmud Sanhedrin 100a. This isn't in the Quran, but it nevertheless seems to be another myth borrowed by Muhammad.
He incorrectly implied that Christians believed the Trinity was composed of the Father, the Son, and Mary (Surah 5:116), but in reality Christians believed the Trinity was composed of the Father, the Son, and the Holy Spirit as Jesus said in Matthew 28:19. Now it should be noted that in an attempt to pardon Muhammad of his mistake, some Muslims will claim that this verse was just referring to a belief that some Christians held at the time of Muhammad. However, this claim is clearly false because the verse says that the belief occurred during the time of Jesus because in the verse Allah asked Jesus whether he had told the people to worship himself and Mary as gods. So clearly, if Allah was talking to Jesus it had to be during the time of Jesus.
Therefore, this verse shows Muhammad incorrectly claimed that during Jesus' time, not during his own time, Christians believed Mary was part of the Trinity.
Muhammad's Plagiarism of the Bible:
Not only did Muhammad use heretical false gospels, Christian forgeries, and Jewish legends in his teachings, but he also plagiarized from the Bible as well. In the Quran and Hadith, there are multiple examples of Muhammad stealing Biblical teachings and principles and acting like it was a revelation he had received himself. Muhammad even used a threat of divorce first made by his close companion (Umar) toward his wives and then acted like it was a revelation from God. Below is a list of some of Muhammad's plagiarism of the Bible:
In Surah 7:40 Muhammad plagiarized from Mark 10:15 and Luke 18:25 about a camel passing through the eye of a needle.
In Sahih Al-Bukhari 93:589 Muhammad plagiarized from 1 Corinthians 2:9, which is one of the letters the Apostle Paul wrote to the Corinthian church. This is really interesting considering how Muslims often incorrectly claim that Paul corrupted the message of Jesus.
In Sahih Al-Bukhari 93:559 Muhammad told a story that is extremely similar to Jesus' parable in Matthew 20:1-16 about the laborers in the vineyard.
After Muhammad's wives were backing each other against Muhammad out of jealousy, Umar threatened them with the possibility of Muhammad divorcing them and getting better wives. As it turns out, Muhammad then received a revelation in Surah 66:5 that just so happens to say the same thing that Umar said.
In Sunan Abu Dawud 3892 (Dar-us-Salam reference) Muhammad said a prayer that is strikingly similar to the one Jesus prayed in Matthew 6:9-13 that is commonly called "The Lord's Prayer" (this Hadith in Sunan Abu Dawud is rated Da'if (weak), so it's possible this Hadith isn't authentic).
It is amazing how the Quran (which is supposed to be verbatim the word of God) relied so much on forgeries, false gospels, mistakes, and lies for information. These fake accounts and false gospels were written by liars to deceive people, yet they ended up in Muhammad's supposed "revelations" of the word of God. Strange, isn't it?
 Oddbjørn Leirvik, Images of Jesus Christ in Islam, 2nd edition (London: Continuum International Publishing Group, 2010), 66.