Narrated `Aisha and Ibn `Abbas: On his death-bed Allah's Messenger (ﷺ) put a sheet over his-face and when he felt hot, he would remove it from his face. When in that state (of putting and removing the sheet) he said, "May Allah's Curse be on the Jews and the Christians for they build places of worship at the graves of their prophets." (By that) he intended to warn (the Muslim) from what they (i.e. Jews and Christians) had done.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنِي بِشْرُ بْنُ مُحَمَّدٍ، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنِي مَعْمَرٌ، وَيُونُسُ، عَنِ الزُّهْرِيِّ، قَالَ أَخْبَرَنِي عُبَيْدُ اللَّهِ بْنُ عَبْدِ اللَّهِ، أَنَّ عَائِشَةَ، وَابْنَ، عَبَّاسٍ رضى الله عنهم قَالاَ لَمَّا نَزَلَ بِرَسُولِ اللَّهِ صلى الله عليه وسلم طَفِقَ يَطْرَحُ خَمِيصَةً عَلَى وَجْهِهِ، فَإِذَا اغْتَمَّ كَشَفَهَا عَنْ وَجْهِهِ، فَقَالَ وَهْوَ كَذَلِكَ " لَعْنَةُ اللَّهِ عَلَى الْيَهُودِ وَالنَّصَارَى، اتَّخَذُوا قُبُورَ أَنْبِيَائِهِمْ مَسَاجِدَ ". يُحَذِّرُ مَا صَنَعُوا.
sunnah.com