Sahih Muslim 25 a
The Book of Faith
Evidence that the islam of one who becomes muslim on his deathbed is valid, so long as the death thoes have not begun; Abrogation of permission to supplicate for forgiveness for the idolators; Evidence that one who dies an idolator is one of the people of hell and no intervention can save him from that
It is narrated on the authority of Abu Huraira that the Messenger of Allah said to his uncle at the time of his death: Make a profession of it that there is no god but Allah and I will bear testimony (of your being a Muslim) on the Day of judgment. But he (Abu Talib) refused to do so. Then Allah revealed this verse: " Verily you canst not guide to the right path whom you love. And it is Allah Who guideth whom He will and He knoweth best who are the guided" (xxviii. 56).