the disbeliever. Islam is supreme, and nothing is supreme over it. These are textual and rational proofs that a Muslim is not executed for killing a disbeliever.
His statement, “Nor is a free person [executed] for a slave,” means that a free person is not executed for a slave. The scholars differ concerning this issue. The position of the school is that a free person is not executed for a slave, because the free person is more complete in status than the slave: a slave may be bought and sold, and his blood-money is his value. Thus, that which may be bought and sold cannot be equivalent to a free person. They cite hadiths in support of this, but they are weak, including: “A free person is not executed for a slave” (1).
For this reason, Abu Hanifah and Shaykh al-Islam Ibn Taymiyyah—and this is also one narration from Ahmad—held that a free person is executed for a slave, based on the general wording of the Prophet’s saying, “The blood of the believers is equal, and the least of them may grant protection on behalf of them all” (2). This view is the correct one.
His statement, “The reverse is subject to execution,” means that a disbeliever is executed for a Muslim, on account of the general proofs establishing retribution. Likewise, a slave is executed for a free person, based on the general proofs. If a slave is executed for another slave by the explicit text of the Quran—“and a slave for a slave” [al-Baqarah 2:178]—then his execution for a free person is all the more warranted. Likewise, a slave is executed for his owner: if a slave owned by a mukātab kills his master, he is executed in retaliation for him, because he is inferior to him.
His statement, “A male is executed for a female, and a female for a male,” is based on the general purport of His words: