Muslims do believe that Mary did not lay with man. But they don't believe that Jesus was the son of god. Rather that he a specially marked human prophet. The most clear cut verse that places Jesus among the mortals that I can see is this: They do blaspheme who say: 'Allah is Christ the son of Mary.' But said Christ: 'O Children of Israel! Worship Allah, my Lord and your Lord.' Whoever joins other gods with Allah, Allah will forbid him the Garden, and the Fire will be his abode. There will for the wrongdoers be no one to help

Theis verse is also interesting for the way it mentions the Trinity by name: O People of the Book! commit no excesses in your religion: nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) A Messenger of Allah, and His Word, which He bestowed on Mary, and a Spirit proceeding from Him: so believe in Allah and His Messengers. Say not "Trinity": desist: it will be better for you: for Allah is One Allah: glory be to Him: (far Exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs.

Jay