Musnad Ahmad 30:3673

Yahya ibn Adam narrated to us, Qutbah narrated to us, from al-A’mash, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Al-Madinah is a sanctuary. 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 on the Day of Resurrection any obligatory deed (sarf) or supererogatory deed (adl)."