Musnad Ahmad 1153:2334

Ya'qub narrated to us, he said: My father narrated to us, from Salih, he said: Ibn Shihab said: Ubayd Allah ibn Abd Allah ibn Utbah narrated to me, that Aisha and Abd Allah ibn Abbas said: When the Messenger of Allah (peace and blessings of Allah be upon him) was overcome by death, he began to cast a khamisa (a garment) over his face. When he felt distressed, he would uncover it from his face. He said, while in that state: "The curse of Allah be upon the Jews and the Christians; they took the graves of their prophets as places of worship." He was warning them against what they had done.