Surah Al-Inshiqaq 84:18
وَٱلْقَمَرِ إِذَا ٱتَّسَقَ
And [by] the moon when it becomes full
Translation: Saheeh International
Tafsir
and by the moon when it is at the full and its light is complete and this happens during the nights of the full moon
Excerpt from Tafsir al-Jalalayn, commentary on 84:18, via Quran.com. The reader has the full commentary and 9 more tafsirs.