Yazid bin Sharik bin Tariq (May Allah be pleased with him) said

I saw 'Ali (May Allah be pleased with him) giving a Khutbah (sermon) from the pulpit and I heard him saying: "By Allah, we have no book to read except Allah's Book and what is written in this scroll. He unrolled the scroll which showed a list of what sort of camels to be given as blood-money, and other legal matters relating to killing game in the sanctuary of Makkah and the expiation thereof. In it was also written: The Messenger of Allah (ﷺ) said: 'Al-Madinah is a sanctuary from 'Air to Thaur (mountains). He who innovates in this territory new ideas in Islam, commits a sin therein, or shelters the innovators, will incur the Curse of Allah, the angels, and all the people, and Allah will accept from him neither repentance nor a ransom on the Day of Resurrection. The asylum (pledge of protection) granted by any Muslim (even of the) lowest status is to be honoured and respected by all other Muslims, and whoever betrays a Muslim in this respect (by violating the pledge) will incur the Curse of Allah, the angels, and all the people; and Allah will accept from him neither repentance nor a ransom on the Day of Resurrection. Whoever attributes his fatherhood to someone other than his (real) father, and takes someone else as his master other than his (real) master without his permission, will incur the Curse of Allah, the angels and all the people, and Allah will accept from him neither repentance nor a ransom on the Day of Resurrection."

[Al-Bukhari and Muslim].