Surah Al-Inshiqaq 84:16
فَلَآ أُقْسِمُ بِٱلشَّفَقِ
So I swear by the twilight glow
Translation: Saheeh International
Tafsir
So I swear fa-lā lā is extra by the twilight al-shafaq the reddishness visible in the horizon after the sunset
Excerpt from Tafsir al-Jalalayn, commentary on 84:16, via Quran.com. The reader has the full commentary and 9 more tafsirs.