Musnad Ahmad 30:3584

Sakan ibn Nafi' narrated to us, Salih narrated to us, from al-Zuhri, who said: Sa'id ibn al-Musayyib informed me that Abu Hurayrah said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "May Allah fight the Jews and the Christians; they took the graves of their prophets as places of worship."