Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 52
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 52, with English translation by Maimonides (Rambam).
לחוג ברגלים, שנאמר: "שָׁלֹשׁ רְגָלִים תָּחֹג לִי" (שמות כג, יד).
To celebrate on the festivals, as [Exodus 23:14] states: "And you shall celebrate three festivals for Me."