Ibn Warraq

The very notion of apostasy has vanished from the West where one would talk of being a lapsed Catholic or non-practising Christian rather than an apostate. There are certainly no penal sanctions for converting from Christianity to any other religion. In Islamic countries, on the other hand, the issue is far from dead.

Koran
It is clear quite clear that under Islamic Law an apostate must be put to death. There is no dispute on this ruling among classical Muslim or modern scholars, and we shall return to the textual evidence for it. Some modern scholars have argued that in the Koran the apostate is threatened with punishment only in the next world, as for example at XVI.106, "Whoso disbelieveth in Allah after his belief -save him who is forced thereto and whose heart is still content with the Faith but whoso findeth ease in disbelief: On them is wrath from Allah. Theirs will be an awful doom." Similarly in III.90-91, "Lo! those who disbelieve after their (profession of) belief, and afterward grow violent in disbelief, their repentance will not be accepted. And such are those who are astray. Lo! those who disbelieve, and die in disbelief, the (whole) earth full of gold would not be accepted from such an one if it were offered as a ransom (for his soul).Theirs will be a painful doom and they will have no helpers."