Surah Ar-Rum 30:6

وَعْدَ ٱللَّهِ ۖ لَا يُخْلِفُ ٱللَّهُ وَعْدَهُۥ وَلَـٰكِنَّ أَكْثَرَ ٱلنَّاسِ لَا يَعْلَمُونَ

[It is] the promise of Allāh. Allāh does not fail in His promise, but most of the people do not know.

Translation: Saheeh International

Tafsir

The promise of God wa‘da’Llāhi is the verbal noun substituting for the full verbal construction; it is actually wa‘adahumu’Llāhu al-nasr ‘God promised them victory’. God does not fail His promise of such help but most people namely the disbelievers of Mecca are not aware of His promise to help them to victory.

Excerpt from Tafsir al-Jalalayn, commentary on 30:6, via Quran.com. The reader has the full commentary and 9 more tafsirs.