Yet Ismaeel was the firstborn, and his mother was Hajar. Now Sara had given Hajar to Abraham as a gift, and then he freed her and married her with full rights. Another interesting point was this, Hajar was given to Sara by a King I believe and Hajar was his daughter. (so actually she was a princess )who was given as a gift to Sara, which she gave to Abraham.( whom he freed and married)
And Ismaeel was the first born son, and claims to justify slavery of the Arabs, or that non arabs are better ( jews) is a innovation which has been placed in the Bible.