بُلُوغُ الْمَرَامِ
Bulugh al-Maram 253
The Book of Prayer
وَلَهُمَا : مِنْ حَدِيثِ عَائِشَةَ -رَضِيَ اَللَّهُ عَنْهَا- : { كَانُوا إِذَا مَاتَ فِيهِمْ اَلرَّجُلُ اَلصَّالِحُ بَنَوْا عَلَى قَبْرِهِ مَسْجِدًا } وَفِيهِ : { أُولَئِكَ شِرَارُ اَلْخَلْقِ } [1]
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."
Sunnah.com reference: Book 2, Hadith 125