(Numbers 27:7:) "You shall surely give them <a possession of an inheritance among the brothers of their father>." Give them movable property, and their father's birthright in the assets of Hepher. They took three portions: the portion of their father, who was among those who came out of Egypt; and his portion with his brothers in the assets of Hepher; and since he was a firstborn, he took two portions.
Zelophehad's Daughters Inherit Three Portions in Hepher's Estate
Midrash Tanchuma Buber, Pinchas 9:3
נתון תתן להם (שם). תן להם מטלטלין, ובכורת אביהן בנכסי חפר נטלו שלשה חלקים, לק אביהם שהיה מיוצאי מצרים, וחלקו עם אחיו בנכסי חפר ושהיה בכור נטל שני חלקים.