Hadith #4443, Kitab al-Maghazi (Military Expeditions of the Prophet Muhammad), Sahih al-Bukhari:
Narrated from 'Ubaydullah bin 'Abdullah bin 'Utba, 'Aisha, and 'Abdullah ibn 'Abbas, may God be pleased with them: They said: "When God's Messenger became seriously ill, he started to cover his face with his woolen sheet, and when he felt short of breath, he removed it from his face and said, "That (this) is so. May God curse (God's curse) be upon the Jews and the Christians [who have taken] took the graves of their prophets [as] places of worship; he intended to warn [the Muslims against] what they had done."
This hadith is mawquf (attributed to one of the Sahaba). A version of this hadith also appears in Sahih Muslim.