Musnad Ahmad 1883

It was narrated from "Abdullah bin ‘Abbas and from "A"ishah that they said: When the Messenger of Allah (ﷺ) became very sick, he covered his face with a cloth, then when he got distressed we removed it from him, and he was saying: “May Allah curse the Jews and the Christians; they took the graves of their Prophets as places of worship.” "A"ishah said: He was warning them [the Muslims] against doing what they [the Jews and Christians] did.