It is narrated from Sayyiduna Abu Umamah bin Tha'labah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever attributes himself to anyone other than his true patrons (who freed him), upon him is the curse of Allah, the angels and all the people; neither repentance nor ransom will be accepted from him. And whoever swears a false oath beside this pulpit of mine, seeking thereby to seize the wealth of a Muslim unjustly, upon him is the curse of Allah, the angels and all the people; neither repentance nor ransom will be accepted from him. And whoever introduces an innovation in this city of mine, or gives shelter to one who introduces an innovation, upon him is the curse of Allah, the angels and all the people; Allah will accept from him neither repentance nor ransom."
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 791