Sahih Bukhari | Volume 7 | Hadith Number 706
Narrated by 'Aisha and 'Abdullah bin 'Abbas
When the disease of Allah's Apostle got aggravated, he covered his face with a Khamisa, but when he became short of breath, he would remove it from his face and say, "It is like that! May Allah curse the Jews Christians because they took the graves of their prophets as places of worship." By that he warned his follower of imitating them, by doing that which they did.