- Circumcision of an eight day old boy supersedes Shabbat, but not of an adult or a child older than eight days.
- Public sacrifice (when the Temple stood) supersedes Shabbat
but no other sacrifice does
- The cutting away of a leprous spot does NOT supersede Shabbat – but if one appears on the foreskin of an eight day old boy, the foreskin may be cut on Shabbat – because circumcision supersedes.
And – as another example of where a positive command supersedes a negative one:
- the placing of fringes on a tallit supersedes the injunction against “mixed cloths” (kil’ayim - Deut. 22:11f) – that is woolen tzitzit may be placed on a linen tallit.