Reference for Bekhorot 4:38

עד כאן לא קאסרי רבנן אלא בשבורה דפסקה מיניה אבל שלמה דלא פסקה מיניה שרו

because he [the Israelite] will not come to confuse it with another animal and sell it [to a heathen], but in the case of a whole animal,<span class="x" onmousemove="('comment',' As in our query, he may think that it is permissible to sell to a gentile a whole animal, since here, too, we allow him to sell an animal for its future offspring.');">²¹</span>

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