We know sacrifices were offered - in the case of burnt offerings, put on the fire- in the Beit HaMikdash on Shabbat and Yom Tov, in fact extra ("Mussaf") offerings were made on such days. In addition to the melacha of bishul performed by the Kohanim setting the offerings on the fire, they presumably also ritually slaughtered the animals on Shabbat itself. Clearly this was permitted. What halachic mechanism allowed them to perform this melacha on Shabbat, when our very notion of melacha comes from an equally sacred task, the building of the Mishkan? Please note that at issue here is a source providing halachic justification for offering korbanot on Shabbat, not the underlying reasoning or philosophical underpinning of such justification (though the latter is certainly welcome).