Da'at, which is Zeir Anpin that unites Chochmah and Binah that are Aba and Ima
Rabbi Shimon begins by saying that the father, mother and son are called Chochmah, Binah and Da'at, and he explains why this is so. He tells us that Da'at receives his father's and mother's inheritance.
88. These father, mother and son are called Chochmah, Binah and Da'at. For when the son, ZEIR ANPIN, receives his father's and mother's tokens, THAT IS, WHEN HE TAKES AND INCLUDES WITHIN HIM CHOCHMAH AND BINAH OF ABA AND IMA, he is called Da'at, WHICH IS DERIVED FROM TESTIMONY (HEB. EDUT), because he bears testimony about both of them BY INCLUDING WITHIN HIM THE MOCHIN OF ABA AND IMA, AS DA'AT RECONCILES AND INCLUDES CHOCHMAH AND BINAH. This son, DA'AT, is called a firstborn SON, as it is written, "Yisrael is My son, My firstborn" (Shemot 4:22), SINCE ZEIR ANPIN, WHO IS DA'AT, IS CALLED YISRAEL, AND IT SAYS OF HIM, "YISRAEL IS MY SON, MY FIRSTBORN." Since he is considered a firstborn he receives two portions, A PORTION FROM ABA, WHO IS CHOCHMAH, AND A PORTION FROM IMA, BINAH. When he gets bigger with his crowns, he receives three portions, CHOCHMAH, BINAH AND DA'AT. In either case, two parts or three parts are all the same, SINCE DA'AT IS NO MORE THAN THE INCLUSION OF CHOCHMAH AND BINAH, IN SUCH A WAY THAT EVEN IN CHOCHMAH, BINAH AND DA'AT THERE ARE NO MORE THAN TWO, CHOCHMAH AND BINAH. Both are the same, BECAUSE DA'AT receives his father's and mother's inheritance, AND HENCE HAS ONLY CHOCHMAH AND BINAH LIKE HIS FATHER AND MOTHER, BUT NO MORE.