Reference for Kiddushin 48:19

ותנא תונא תמות וזכרות בבהמה ואין תמות וזכרות בעופות

R'Simeon B'Gamaliel said: and he destroy it<span class="x" onmousemove="('comment',' Ex. XXI, 26.');">³⁴</span> [implies], only when he intends to destroy. And the Rabbis: how do they employ 'and he destroy it'? - They need it for what was taught: R'Eleazar said: If he inserts his hand in his bondmaid's womb<span class="x" onmousemove="('comment',' Lit., 'bowels' - in order to deliver her of child.');">³⁵</span>

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