Maimonides on the Monotheism of Muslims

"The Ishmaelites are not at all idolaters; [idolatry] has long been severed from their mouths and hearts; and they attribute to God a proper unity, a unity concerning which there is no doubt. And because they lie about us, and falsely attribute to us the statement that God has a son, there is [nevertheless] no reason for us to lie about them and say that they are idolaters... And should anyone say that the house that they honor [the Ka`abah] is a house of idolatry and an idol is hidden within it, which their ancestors used to worship, then what of it? The hearts of those who prostrate toward it today are [directed] only toward Heaven . . . [Regarding] the Ishmaelites today - idolatry has been severed from the mouths of all of them [including] women and children. Their error and foolishness is in other things which cannot be put into writing because of the renegades and wicked among Israel [koferim/apostates]. But as regards the unity of God they have no error at all." Maimonides (the Rambam) in his responsum to `Obadyah the proselyte."

"'Ummatun Qā'imatun"

They are not all alike from the People of the Book (Ahl al-Kitāb, People of the Bible or Tanakh). There is an Upright Ummah ('Ummatun Qā'imatun); they recite Allah's ayat in the nighttime and they prostrate (Yasjudūna). (Qur'ān 3.113)

لَيْسُوا سَوَاءً ۗ مِنْ أَهْلِ الْكِتَابِ أُمَّةٌ قَائِمَةٌ يَتْلُونَ آيَاتِ اللَّهِ آنَاءَ اللَّيْلِ وَهُمْ يَسْجُدُونَ