While New Testament authors cite the Old Testament at least 263 times in their writings, Muhammad quotes the Bible (Exodus 21:23-25, cf. Sura 5:45) only partially and only once in his entire Quran. This is certainly strange for a man who claimed to be following the traditions of the prophets of the God of Israel, Who had said a lot of extremely important things over four and a half millennia.
Instead, Muhammad appears to have taken his teachings from a variety of sources, the large majority of them unreliable. He borrowed from Arabian fables. He borrowed from Christian heretical sources such as the Gnostic Gospels. But he also borrowed from the Jewish Talmud.
One particular Quranic ayah (verse) has gained popularity among Muslims who find themselves having to defend their faith as a "religion of peace" on the Internet. It is known to them as Surat Al-Mā'idah ayah 32, which says:
“... if anyone killed a person... it would be as if he killed all mankind, and if anyone saved a life, it would be as if he saved the life of all mankind." Qur'an 5:32 (Khan)
But what many Muslims do not know is that this quotation comes from the Jewish Talmud and predates Muhammad by over 300 years.
"Whoever destroys a soul, it is considered as if he destroyed an entire world. And whoever saves a life, it is considered as if he saved an entire world." Mishnah, Sanhedrin 4:5; Babylonian Talmud Tractate Sanhedrin 37a
The Talmud is a collection of the opinions of thousands of Jewish rabbis and their discussions on issues of Jewish law, history and other such topics. It is not by any means considered -- even by Jews -- as inspired by God in the same way that He inspired the Bible.
Hence, the question. Why did Allah borrow a quotation from Jewish rabbis instead of quoting the Bible which, presumably, he had written? As intelligent as some men might be, the Bible is clear about God being far wiser than anyone who has ever existed.
So why did Allah need to plagiarize from the Jewish Talmud and other sources to fill up his Quran?
That's one more of many things about the Quran and Islam that make you go, "Hmmmm..."
Jesus is Lord!