Surah 91. Ash-Shams, Ayah 2

Lit., "as it follows it (talaha)", i.e., the sun. According to the great philologist Al-Farra', who lived in the second century after the hijrah, "the meaning is that the moon derives its light from the sun" (quoted by Razi). This is also Raghib's interpretation of the above phrase.

 Or “… when it reflects the sun’s light.”

The first pair is the glorious sun, the source of our light and physical life, and the moon which follows or acts as second to the sun for illuminating our world. The moon, when she is in the sky with the sun, is pale and inconspicuous; in the sun's absence she shines with reflected light and may metaphorically be called the sun's vicegerent. So with Revelation and the great Prophets who brought it; and the minor Teachers who derive their light reflected, or perhaps doubly reflected, from the original source.