Reference for Bekhorot 52:36

(שמות כב, כח) בכור בניך תתן לי כן תעשה לצאנך

Scripture adds [the duty of] another doing<span class="x" onmousemove="('comment',' The superfluous text 'Thou shalt do' denotes that in the case of an ox and large cattle in general, a longer period of doing for the animal is demanded than is the case with sheep.');">²¹</span>

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