Midrash for Bava Batra 253:2
רב שיזבי אמר אף אינו נימול לשמנה דאמר קרא (ויקרא יב, ב) אשה כי תזריע וילדה זכר וביום השמיני ימול עד שיהא זכר משעת לידה
at the time of [his] birth.<span class="x" onmousemove="('comment',' Emphasis is laid on born and sons, in the text cited. ');"><sup>4</sup></span> R. Shezbi said: Nor is he circumcised on the eighth [day<span class="x" onmousemove="('comment',' V. Gen. XVII, 12. ');"><sup>5</sup></span> of his birth];<span class="x" onmousemove="('comment',' If that day fell on a Sabbath. ');"><sup>6</sup></span> for Scripture said, <i>If a woman be delivered, and bear a man-child … and in the eighth day [the flesh of his foreskin] shall be circumcised</i>,<span class="x" onmousemove="('comment',' Lev. XII, 2-3, from which is derived the suspension of the Sabbath laws in favour of circumcision on the eighth day (v. Shab. 131b). ');"><sup>7</sup></span>