‘Ā'ishah (may Allah be pleased with her) reported: As the Messenger of Allah (may Allah’s peace and blessings be upon him) was about to breathe his last, he kept drawing his sheet upon his face, and when he felt uneasy, he would uncover his face and say in that very state: "May the curse of Allah be upon the Jews and the Christians, for they took the graves of their prophets as places of worship - He wanted to warn against what they did." If it were not for that, his grave would be made prominent; yet, he feared it might be taken as a place of worship.
شرح الحديث :
In this Hadīth, ‘Ā'ishah (may Allah be pleased with her) informs us that the Prophet (may Allah's peace and blessings be upon him) said while in the throes of death: “May the curse of Allah be upon the Jews and the Christians.” This is because they built places of worship over the graves of their prophets. From the Prophet’s statement, ‘Ā'ishah (may Allah be pleased with her) concluded that he wished to warn his Ummah against falling into the same error, building a mosque over his grave. Then, she clarified that the Companions (may Allah be pleased with them) did not bury the Prophet (may Allah's peace and blessings be upon him) outside his room for fear that his grave might be taken as a place of worship.