Reference for Shabbat 270:12

אמר רב משרשיא בלוקח שפחה ע"מ שלא להטבילה

But how can [a slave] born in the house be found who is circumcised on the first day?<span class="x" onmousemove="('comment',' Since he rejects the distinction based on when the mother had her ritual bath, one born in the house is certainly similar to a Jew. ');"><sup>12</sup></span>