Reference for Bava Batra 247:5
ורבי אומר אמר קרא פי שנים מקיש חלק בכורה לחלק פשוט מה חלק פשוט אע"ג דלא מטא לידיה אף חלק בכורה אע"ג דלא מטא לידיה
But Rabbi maintains, [since] Scripture says, a double portion,<span class="x" onmousemove="('comment',' Ibid. The portion of the birthright and the ordinary portion were included in one expression. ');"><sup>13</sup></span> the portion of the birthright [is to be] compared to the ordinary portion; as the ordinary portion [is his] although it has not yet come into his [father's] possession,<span class="x" onmousemove="('comment',' I.e., prospective property. v. supra. ');"><sup>14</sup></span> so [is] the portion of the birthright although it has not yet come into his possession. But [as to] the Rabbis also, surely it is written, a double portion? — That [expression indicates that the two portions] to be given to him are to adjoin one another.<span class="x" onmousemove="('comment',' Lit., 'on one boundary' — both portions being treated as one. ');"><sup>15</sup></span>