Narrated Aisha (radhi Allaahu anha) and Abdullaah bin Abbaas (radhi Allaahu anhu) :
When the last moment of the life of Allaah’s Messenger (Sallallaahu Alaihi Wasallam) came, he started putting his Khameesa (a woolen blanket) on his face and when he felt hot and short of breath he took it off his face and said, “May Allaah curse the Jews and Christians, for they built places of worship at the graves of their Prophets.”
[The Prophet (Sallallaahu Alaihi Wasallam) was warning (Muslims) of what those people had done].
[Saheeh Al-Bukhari, Hadeeth No. 427, Vol. 1]
Source :The Book of Mosques and places of worship – Chapter 3 – It is forbidden to build mosques over the graves
Al-Lulu Wal-Marjan, Compiled by : Fuwad Abdul-Baqi, Translated by : Dr. Muhammad Muhsin Khan