R. Yishmael says: We did not learn that work is forbidden on the intermediate days of a festival. Whence do we derive that it is, indeed, forbidden: From "six days shall you eat matzoth and on the seventh day is a holding back" — Just as the seventh day is "held back," so the six days are "held back."
— But perhaps (the intent is:) just as the seventh day is held back from all work, so the six days are held back from all work! It is, therefore, written "Six days shall you eat matzoth and on the seventh day is a holding back for the L-rd your G-d. You shall do no work" — the seventh day is held back from all work, and not the six days" — whence we derive that Scripture relegated it to the sages to rule which day is forbidden and which day is permitted, which labor is forbidden and which labor is permitted.