Islam's Qur'an, in Sura 2 verse 256 says this: "There shall be no compulsion in [acceptance of] the religion. The right course has become clear from the wrong." If Muslims truly believe that the Qur'an is the word of Allah, then it seems clear they would live out what that simple verse says and not force people to convert to Islam or punish people when they leave that religion.
But yet, that is exactly not what the theocratic government of Iran is doing in its attempt to murder Pastor Youcef Nadarkhani for his renouncement of Islam and his acceptance of Christianity. CNN recently had an interesting article on the debate between Islamic scholars over the situation, but in the end, it seemed most agreed that Iran is wrong in its stance on Pastor Youcef. An exposition of the Qur'an's verse 256 sides with Youcef too.
Continue to pray for Pastor Youcef's release and for the safety of him and his family.