Reference for Bava Batra 248:9

ואלא הא דתניא ירשו שטר חוב בכור נוטל פי שנים בין במלוה בין ברבית מני לא רבי ולא רבנן

excludes<span class="x" onmousemove="('comment',' The firstborn is not entitled to a double portion. ');">¹²</span> the [natural] appreciation of an estate [that accrued] after the death of their father, and much less is he [entitled] to take [a double portion in] the appreciation which the heirs produced after the death of their father. And who is [the author of this statement]? — The Rabbis.

Jastrow

Jastrow

Jastrow

Jastrow