Jerusalem Talmud Bava Batra 8.3

משנה: אֶחָד הַבֵּן וְאֶחָד הַבַּת בַּנַּחֲלָה אֶלָּא שֶׁהַבֵּן נוֹטֵל פִּי שְׁנַיִם בְּנִיכְסֵי הָאָב וְאֵינוֹ נוֹטֵל פִּי שְׁנַיִם בְּנִיכְסֵי הָאֵם. וְהַבָּנוֹת נִיזּוֹנוֹת מִנִּיכְסֵי הָאָב וְאֵינָן נִיזּוֹנוֹת מִנִּיכְסֵי הָאֵם.

MISHNAH: Both son and daughter are equal for the rules of inheritance, except that the son take a double portion of the father’s property but no double portion of the mother’s property. And the daughters can claim sustenance from the father’s property but not from the mother’s property.

הלכה: אֶחָד הַבֵּן וְאֶחָד הַבַּת בַּנַּחֲלָה כול׳. כָּתוּב בְּכָל אֲשֶׁר יִמָּצֵא לוֹ וגו׳. כֵּיצַד יוֹרֵשׁ בָּרָאוּי כְּבַמּוּחְזָק. כֵּיצַד. מֵת אָבִיו בְּחַיֵּי אֲבִי אָבִיו נוֹטֵל פִּי שְׁנַיִם מִנִּיכְסֵי אָבִיו וְאֵין נוֹטֵל פִּי שְׁנַיִם מִנִּיכְסֵי אֲבִי אָבִיו. וְאִם הָיָה אָבִיו בְּכוֹר כְּשֵׁם שֶׁנָּטַל מִנִּכְסֵי אָבִיו כָּךְ נוֹטֵל בְּנִיכְסֵי אֲבִי אָבִיו. רֵישׁ לָקִישׁ בְּשֵׁם אַבָּא בַּר דְּלָיָיה. נֶאֱמַר מִשְׁפָּט לְעִנְיַין כְּפֵילָה וְנֶאֱמַר מִשְׁפָּט לְעִנְיַין פְּשׁוּטָה. מַה לְעִנְיַין פְּשׁוּטָה אַתְּ רוֹאֶה אֶת הַבֵּן כִּילּוּ קַיָים לִיטּוֹל פְּשִׁיטוּת אָבִיו. אַף לְעִנְיַין כְּפֵילָה אַתָּה רוֹאֶה אֶת הַבֵּן כִּילּוּ קַיָים לִיטּוֹל כְּפֵילַת אָבִיו.

HALAKHAH: “Both son and daughter are equal for the rules of inheritance,” etc. It is written: “Of anything which will be found with him,” etc. How could he inherit the expectancy like existing property? How? If his father died during his father’s father’s lifetime, he takes a double portion of his father’s estate but not a double portion of his grandfather’s estate. But if his father was a firstborn, just as he takes from his father’s estate so he takes from his grandfather’s estate. Rebbi Simeon ben Laqish in the name of Abba [Cohen] bar Delaiah: It was said “a rule of law” in the matter of a double portion just as it was said “a rule of law” in the matter of a single portion. Since for a single portion one considers the son as if he were alive to take his father’s single portion so for a double portion one considers the son as if he were alive to take his father’s double portion.