It is narrated from Hazrat Aisha (may Allah be pleased with her) 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 Christians; they made the graves of their prophets (peace be upon them) places of prostration." Hazrat Aisha (may Allah be pleased with her) says that in fact, the Prophet (peace and blessings be upon him) was warning people against this action so that they would not fall into it.