"In light of the texts (Qur'an and prophetic traditions) and the way the Prophet behaved with the people who left Islam (like Hishâm and 'Ayyash) or who converted to Christianity (such as Ubaydallah ibn Jahsh), it should be stated that one who changes her/his religion should not be killed. In Islam, there can be no compulsion or coercion in matters of faith not only because it is explicitly forbidden in the Qur'an but also because free conscious and choice and willing submission are foundational to the first pillar (declaration of faith) and essential to the very definition of "Islam". Therefore, someone leaving Islam or converting to another religion must be free to do so and her/his choice must be respected." (Tariq Ramadan on Apostasy)


Both Ibrahim al-Nakha'i  and Sufyan al-Thawri were of the view the apostate should be re-invited to Islam, but should never be condemned to death.

Source:  Chapter: Freedom of Religion in Mohammad Hashim Kamali’s Freedom of Expression in Islam Islamic Text Society, 1997

Also I think you might find this link useful it's sites various various respected scholars showing that apostasy is not punishable under Sharia