Narrated Anas:
The Prophet (s.a.w.a.) said, "Medina is a sanctuary from that place to that. Its trees should not be cut and no heresy should be innovated nor any sin should be committed in it, and whoever innovates in it an heresy or commits sins (bad deeds), then he will incur the curse of Allah, the angels, and all the people." (See Hadith No. 409, Vol 9).
'Asim reported:
I asked Anas b. Malik whether Allah's Messenger (s.a.w.a.) had declared Medina as sacred. He said: Yes. (the area) between so and so. He who made any innovation in it, and further said to me: It is something serious to make any innovation in it (and he who does it) there is upon him the curse of Allah, and that of the angels and of all the people, Allah will not accept from him on the Day of Resurrection either obligatory acts or the supererogatory acts. Ibn Anas said: Or he accommodates an innovator.