Halakhah su Levitico 23:21

The commandment of resting from work on the day of [Shavuot]: To rest from all work on the sixth day of Sivan - and this is called the festival of Shavuot (Weeks) - except for that which is specific to the needs of the eating of the soul as it is stated (Leviticus 23:21), "And you shall call on that very day, a holy occasion." And I have already written in the commandment of resting on the first day of Pesach in this Order (Sefer HaChinukh 297) that in any place about which it is stated in the Torah, "a holy occasion," its content is to say, make it holy, to not do work on it.

To not do work on the day of the holiday of Shavuot: To not do work on the day of [Shavuot] - which is the sixth day of Sivan, as it is stated (Leviticus 23:15-16), "And you shall count for yourselves from the morrow of the Shabbat, etc. you shall count fifty days, etc." And the understanding of "from the morrow of the Shabbat," is meaning to say, the morrow of the first holiday of Pesach, about which it was speaking first. As if it was the Shabbat of creation (the seventh day of the week) - if so, it will not have informed us which. And it comes out that the fifty days end on the sixth of Sivan. How is this? Fifteen days from Nissan, which is always full (consisting of thirty days); and twenty-nine days of Iyar, which is always lacking (consisting of twenty-nine days); and six days of Sivan - behold, [that is] fifty. And this fiftieth day - which was the day that the Torah was given - is the holiday of the Assembly (atseret), and it is also called the holiday of Shavuot (Weeks). And it is also written at the end of the section about this glorious day (Leviticus 23:21), "all work of labor shall you not do" - we have already written that any labor that is not for the needs of food for the soul is called, work of labor.