Musnad Ahmad 32:1596

Mu'ammal narrated to us, Hammad narrated to us, from Humayd and 'Asim al-Ahwal, from Anas, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Al-Madinah is sacred from such-and-such to such-and-such. Whoever commits an innovation (hadath) in it, or shelters an innovator (muhdith), upon him is the curse of Allah, the angels, and all of mankind. Allah will not accept from him any obligatory deed (sarf) or supererogatory deed ('adl)." Hammad said: And Humayd added in it: "No weapon shall be carried in it for fighting."