It is narrated from Abdullah bin Abbas and Aisha (may Allah be pleased with them) that when the Prophet (peace and blessings be upon him) was afflicted with his final illness, he would repeatedly cover his blessed face with a sheet. When he felt discomfort, we would remove the sheet from his face. The Prophet (peace and blessings be upon him) was saying: "May Allah's curse be upon the Jews and the Christians; they made the graves of their prophets places of prostration." Aisha (may Allah be pleased with her) said that in fact, the Prophet (peace and blessings be upon him) was warning people against their actions so that they would not fall into the same practice.