Musnad Ahmad 30:3585

Uthman ibn Umar narrated to us, Malik narrated to us, from al-Zuhri, from Sa'id ibn al-Musayyib, from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "May Allah curse the Jews and the Christians; they took the graves of their prophets as places of worship."