TT #27 · Parshas Tazria · Aliyah 1 · Passuk 3
English: On the eighth day the flesh of his foreskin shall be circumcised.
Chabad.org — Chumash, English translation + Rashi for Vayikra 12:3
Torah Temimah cites Shabbos 135a.
E-Daf — Shabbos 135a · Shas.org · Sefaria — vowelized Shabbos 135a
English: The Sages taught: A definite circumcision obligation overrides Shabbos, but a doubtful case does not.
Limitation by textual precision
Circumcision may override Shabbos only when the obligation is definite, not when the case is doubtful.