Interesting. I'm not the most observant Christian, but I have certainly read the bible more, ever since 9-11 and trying to find my own answers regarding Islam. I completely believe the Bible tells us this. Abraham and Hagars son Ishmael is a story in the Bible.
Genesis 16:12
"He shall be a wild donkey of a man, his hand against everyone and everyone’s hand against him, and he shall dwell over against all his kinsmen.â€
According to the Koran, Mohammed was a direct decendant of Ishmael.