Chagigah 2:4-5

Chagigah 2:4

If Shavuos falls on Friday, Beis Shammai say that the day to slaughter its burnt offerings is after Shabbos (i.e., Sunday), while Beis Hillel say that there is no slaughtering after Shabbos (i.e., it is slaughtered on Friday). They agree that if Shavuos falls on Shabbos, the day to slaughter the burnt offerings is Sunday. When the day to slaughter is postponed, the Kohein Gadol does not wear his special garments, and eulogizing and fasting are permitted. This is done so as not to validate the mistaken (i.e., heretical) opinion that Shavuos must necessarily be the day after Shabbos (based on a faulty interpretation of Leviticus 23:15).

Chagigah 2:5

We ritually wash our hands before eating regular, unsanctified food (chulin), tithes (maaser) and the portion for the kohein (terumah). Before eating sanctified portions (kodesh), one must immerse in a mikvah. When it comes to handling the water with the ashes of the red heifer, if one’s hands have been rendered ritually unclean, then his entire body is ritually unclean (and he must immerse in a mikvah).