Reference for Chullin 281:19

ת"ל תשלח מכל מקום

But there is here, is there not, both a positive and a negative precept?<span class="x" onmousemove="('comment',' The negative precept Thou shalt not take the dam, and the positive precept Thou shalt in any wise let the dam go.');"><sup>13</sup></span>