It is written: (Dan. 12:3) The wise shall radiate (yazhiru), like the radiance (zohar) of the firmament... etc.
These are Rabbi Shim’on ben Yoḥai and his companions: Rabbi El’azar his son, and Rabbi Abba, and Rabbi Yosse, and Rabbi Ḥiya, and Rabbi Yitzḥaq, and the rest of the companions, who radiate radiance [Var. who are radiating] above,... like the radiance of the firmament.
What is meant by ‘like the radiance’? But when they made this composition, it was agreed to on high, and they called it The Book of Radiance (Sepher) ha-Zohar.