one side allies itself with one people and seeks their aid, while the other allies itself with another, leading to grave strife and enmity.
The cause of this is their departure from the course of justice, which requires retaliation in cases of murder. Allah therefore prescribed retaliation for us—which entails equality and equivalence (1)—and informed us that it preserves life by sparing the blood of anyone other than the killer among the kinsmen of both parties.
Moreover, when one who intends to kill knows that he will be put to death, he refrains from killing. It has been narrated from ʿAlī ibn Abī Tālib and ʿAbd Allāh ibn ʿAmr (2), from the Messenger of Allah (may Allah bless him and grant him peace), that he said: “The blood of the believers is equal in value (3). They stand united against all others, and protection granted by the least of them is binding upon them all. Indeed, no Muslim shall be killed in retaliation for a disbeliever, nor shall a person under covenant be killed while his covenant remains in force.” (4) It was narrated by Ahmad, Abū Dāwūd, and other compilers of the Sunan.
Thus, the Messenger of Allah (may Allah bless him and grant him peace) ruled that the blood of all Muslims is equal in value—that is, they are equal and equivalent. No Arab is preferred over a non-Arab, no Qurashī or Hāshimī over any other Muslim, no freeborn person over a manumitted freedman, and no scholar or ruler over an unlearned person or subordinate (5). He likewise ruled that they are equal in matters of property, such as inheritance: sons receive equal shares of their mother’s estate even if they differ in their religious and worldly standing.