صحيح البخاري

Narrated `Ali:

We have no Book to recite except the Book of Allah (Qur'an) and this paper. Then `Ali took out the paper, and behold ! There was written in it, legal verdicts about the retaliation for wounds, the ages of the camels (to be paid as Zakat or as blood money). In it was also written: 'Medina is a sanctuary from Air (mountain) to Thaur (mountain). So whoever innovates in it an heresy (something new in religion) or commits a crime in it or gives shelter to such an innovator, will incur the curse of Allah, the angels and all the people, and none of his compulsory or optional good deeds will be accepted on the Day of Resurrection. And whoever (a freed slave) takes as his master (i.e. be-friends) some people other than hi real masters without the permission of his real masters, will incur the curse of Allah, the angels and all the people, and none of his compulsory, or optional good deeds will be accepted on the Day of Resurrection. And the asylum granted by any Muslim is to be secured by all the Muslims, even if it is granted by one of the lowest social status among them; and whoever betrays a Muslim, in this respect will incur the curse of Allah, the angels, and all the people, and none of his Compulsory or optional good deeds will be accepted on the Day of Resurrection."