Sunnah.com reference : Book 2, Hadith 125English translation : Book 2, Hadith 251Arabic reference : Book 2, Hadith 253
Narrated 'Aishah (RA) in al-Bukhari and Muslim [that Allah's Messenger (ﷺ) said], "When a pious person amongst them (the Jews and Christians) died they used to build a place of worship and prostration on his grave."

In the same Hadith is:
"Those are the worst of creatures."
وَلَهُمَا : مِنْ حَدِيثِ عَائِشَةَ ‏-رَضِيَ اَللَّهُ عَنْهَا‏- : { كَانُوا إِذَا مَاتَ فِيهِمْ اَلرَّجُلُ اَلصَّالِحُ بَنَوْا عَلَى قَبْرِهِ مَسْجِدًا }  وَفِيهِ : { أُولَئِكَ شِرَارُ اَلْخَلْقِ }   1‏‏1 ‏- صحيح .‏ رواه البخاري (427)‏ ، ومسلم (528)‏ .‏