Musnad Ahmad 1153:1898

Al-Zuhri said: Ubayd Allah ibn Abd Allah informed me, saying: Aisha and Ibn Abbas informed me that when the Prophet, peace and blessings of Allah be upon him, was overcome by his final illness, he began to cast a *khamisah* (a garment) of his over his face. When he felt distressed, he would uncover it from his face, while he was saying: "The curse of Allah be upon the Jews and the Christians; they took the graves of their prophets as places of worship." She (Aisha) said: He was warning against what they had done.