Sahih Al-Bukhair Volume 1, Book 8, Hadith # 419
Narrated 'Aisha (RAA) Um Habiba (RAA) and Um Salama (RAA) mentioned about a church they had seen in Ethiopia in which there were pictures. They told the Prophet (SAW) about it, on which he said, "If any religious man dies amongst those people they would build a place of worship at his grave and make these pictures in it. They will be the worst creature in the sight of Allah on the Day of Resurrection."
Sahih Muslim Book 4, Hadith # 2116
Narrated Jabir ibn Abdullah (RAA) Rasulullah (SAW) forbade that the graves should be plastered, or they be used as sitting places (for the people), or a building should be built over them.
Sahih Al-Bkhari Volume 1, Book 8, Hadith # 427
Narrated 'Aisha (RAA) and 'Abdullah bin 'Abbas (RAA) When the last moment of the life of Allah's Apostle (SAW) came he started putting his 'Khamisa' on his face and when he felt hot and short of breath he took it off his face and said, "May Allah curse the Jews and Christians for they built the places of worship at the graves of their Prophets." The Prophet (SAW) was warning (Muslims) of what those had done.
Sahih Al-Bukhari Volume 1, Book 8, Hadith # 428
Narrated Abu Huraira (RAA) Rasulullah (SAW) said, "May Allah's curse be on the Jews for they built the places of worship at the graves of their Prophets."
Sahih Muslim Book 4, Number 1083
Narrated Jundub ibn Abdullah (RAA) "I heard from the Apostle of Allah (SAW) five days before his death and he said: I stand acquitted before Allah that I took anyone of you as friend, for Allah has taken me as His friend, as he took Ibrahim as His friend. Had I taken any one of my Ummah as a friend, I would have taken AbuBakr as a friend. Beware of those who preceded you and used to take the graves of their prophets and righteous men as places of worship, but you must not take graves as mosques;I forbid you to do that.
Sahih Muslim Book 4, Hadith # 2121
Narrated AbuMarthad al-Ghanawi (RAA) Allah's Messenger (SAW) said: Do not sit on the graves and do not pray facing towards them.