Excerpt from Maimonides,
“Letter to Yemen”
concerning Mohammed and Islam
Let Ye understand, my brothers, the Holy One Blessed HE through the trap created by our iniquities cast us amongst this nation, the people of Ishmael [Muslim Arabs] whose oppressiveness is firmly upon us and they connive to do us wrong and despicably downgrade us as the Almighty decreed against us (Deuteronomy 32:31, “Your enemies shall judge you”). There never came against Israel a more antagonistic nation. They oppress us with the most oppressive measures to lessen our number, reduce us, and make us as despicable as they themselves are. King David, may he rest in peace, saw through Divine Inspiration all the calamities that were destined to come upon Israel. Nevertheless [even though he saw all the other troubles], he still began to shout out and lament in the name of the whole nation against the oppression that would be occasioned by the Ishmaelites. David said, “WOE IS ME, THAT I SOJOURN IN MESECH, THAT I DWELL IN THE TENTS OF KEDAR!” [Psalms 120:5].
Notice how David emphasizes “Kedar” out of all the other Children of Ishmael. This is because that Mad Man [Hebrew: “meshuga”] came from Kedar according to what has been published concerning his geneaology.
Maimonides is referring to the fact that Mohammed was from the Koresh clan of Arabs and they claimed descent from Kedar son of Ishmael (Genesis 25:13).
-Maimonides continues to explain from Daniel 8:10 that Ishmael will ultimately be defeated by Israel.
Source: Maimonides, “Letter to Yemen” 1:4.