Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 6
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 6, with English translation by Maimonides (Rambam).
לְדָבְקָה בּוֹ, שֶׁנֶּאֱמָר: "וּבוֹ תִדְבָּק" (דברים י כ).
To cling to Him, as [Deuteronomy 10:20] states: "And you shall cling to Him."