On his death-bed Allah's Messenger (ﷺ) put a sheet over his-face and when he felt hot, he would remove itfrom his face. When in that state (of putting and removing the sheet) he said, "May Allah's Curse beon the Jews and the Christians for they build places of worship at the graves of their prophets." (Bythat) he intended to warn (the Muslim) from what they (i.e. Jews and Christians) had done.