I think there's an Islamic concept know as "People of the Book" or something, which calls for respect and tolerance of faiths founded prior to islam? I think that's it. That would include, obviously, Christians.
Yes, Christians, Jews, and Zoroastrians are lumped together as People of the Book, who, according to Islam, have received incomplete or corrupted but nevertheless authentic prophecies from God and that they aren't to be interfered with. Initially, the lack of such protection for Hindus and Buddhists caused some issues during the Islamic push into India. Either way, Medieval Muslim rulers (especially the Umayyads, who weren't particularly big on piety) were just as happy if their subjects didn't convert because it gave them an excuse to use the
jizya,the special nonbeliever tax rate that helped fund Medieval Islamic states. Especially in Syria and Egypt, even though the territories had been conquered in the mid-7th century in the initial Arab Conquests, it wasn't until the late 10th century that the territories were even majority Muslim, in large part because the Umayyads and to a lesser extent their Abbasid successors weren't keen on eroding their taxbase by making Christians into Muslims.
How much any of the above is relevant today is questionable at best. Only the most reactionary Islamic states still have the jizya, but at the same time, except in famously tolerant countries like Malaysia and Indonesia, Christians in many majority Muslim countries may receive a hard time these days (the reverse also being true). Also, new religions like the Bahai aren't covered by this concept and are still ruthlessly persecuted, especially in the Bahai faith's native Iran.
