Midrash for Sukkah 5:1
הֶחָלִיל חֲמִשָּׁה וְשִׁשָּׁה. זֶהוּ הֶחָלִיל שֶׁל בֵּית הַשּׁוֹאֵבָה, שֶׁאֵינָה דּוֹחָה לֹא אֶת הַשַּׁבָּת וְלֹא אֶת יוֹם טוֹב. אָמְרוּ, כָּל מִי שֶׁלֹּא רָאָה שִׂמְחַת בֵּית הַשּׁוֹאֵבָה, לֹא רָאָה שִׂמְחָה מִיָּמָיו:
The chalil [(There were many different types of instruments there, but because the chalil is heard above the others it receives distinct mention.)] — five and six [sometimes five, sometimes six. If the first day of the festival fell on a Sabbath — six; if on a weekday — five. For it overrides neither Sabbath nor festival.] This is the chalil of simchath Beth Hashoevah, [so called because the entire joy is over the drawing (sheivah) of water for the libation, in keeping with (Isaiah 12:3): "And you shall draw water with joy"], which overrides neither Sabbath nor festival. They said: "Whoever did not see simchath Beth Hashoeva never saw joy in his life."