Maliks Muwatta Book 45, Hadith Number 16.
Section : The Epidemic of Madina.
Yahya related to me from Malik from Nuaym ibn Abdullah al-Mujmir that Abu Hurayra said, “The Messenger of Allah, may Allah bless him and grant him peace, said, ‘There are angels at the entries of Madina, and neither plague nor the Dajjal will enter it.'”