משנה אויף במדבר 28:2

The men of the guard are permitted to drink wine in the evenings but not during the day, but the men of the father’s house may not [drink wine] either on the day or on the preceding evening. Both the men of the guard and the men of the ma'amad may not cut their hair nor wash their clothes, but on Thursday they may [do so] in honor of Shabbat.

What are the ma’amadot? Since it is said, “Command the children of Israel and say to them: My offering, My food” (Numbers 28:2). Now how can a man’s offering be offered and he is not present? [Therefore] the former prophets instituted twenty-four mishmarot (guards). For each mishmar there was a ma’amad [at the Temple] in Jerusalem consisting of priests, Levites and Israelites. When the time came for the mishmar to go up [to Jerusalem] the priests and Levites went up to Jerusalem and the Israelites of that mishmar assembled in their cities and read the story of creation.

These things in [connection with] the pesah override Shabbat: its slaughtering and the sprinkling of its blood and the cleansing of its innards and the burning of its fat. But its roasting and the washing of its innards do not override Shabbat. Carrying it and bringing it from outside the Shabbat border and cutting off its wart do not override Shabbat. R. Eliezer says they do override [Shabbat].