Well, maybe you have to revise your hypothesis, here is why:
This is the outline of the legend taken from Wikipedia:
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The outline of the story is that during the persecutions of the Roman emperor Decius, around 250, seven young men were accused of Christianity. They were given some time to recant their faith, but instead gave their worldly goods to the poor and retired to a mountain to pray, where they fell asleep. The emperor, seeing that their attitude towards paganism had not improved, ordered the mouth of the cave to be sealed.
Decius died in 251 and many years passed during which Christianity went from being persecuted to being the major religion of the Roman Empire. At some later time usually, during the reign of Theodosius II (408 - 450) the landowner decided to open up the sealed mouth of the cave, thinking to use it as a cattle pen. He opened it and found the sleepers inside. They awoke, imagining that they had slept but one day. One of their number returned to Ephesus. He was astounded to find buildings with crosses attached; the townspeople were astounded to find a man trying to spend old coins from the reign of Decius. The bishop was summoned to interview the sleepers; they told him their miracle story, and died praising God.
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You will notice that the legend historical framework is about 250-450 CE. Just this precludes it to be part of the Bible. The parallels in the Qur'an are also very, very close to the legend. Also the legend circulated in Aramaic in the ANE. I do not see any other plausible explanation other than this story, part of Syriac Aramaic Christian literature, was incorporated into the Qur'an.
Yes and no
The legend of Alexandre, which did not have any Biblical origin of course, was combined with material from the Book of Revelation (God & Magog).
Again, we have very, very close material in Aramaic that circulated in the Syriac Church. There are still Aramaic manuscripts in existence.
I think that your hypothesis of a single source (i.e. the Bible) for the Qur'an is as wrong as the traditional Muslim hypothesis of a single source (i.e. a single prophet).
Recent scholarship has shown, I think beyond any shade of doubt, that the most likely scenario is of multiple sources, the bulk of them from the Syriac Church. The Bible was probably only an indirect source of the Qur'an. I think that there are only few direct quotations from the Bible and those could still be explained as coming from Syriac lectionaries.