Surah Adh-Dhariyat 51:5

إِنَّمَا تُوعَدُونَ لَصَادِقٌ

Indeed, what you are promised is true.

Translation: Saheeh International

Tafsir

assuredly what you are promised mā ‘what’ relates to the verbal action in other words the promise given to them of resurrection and other matters is true is indeed a true promise

Excerpt from Tafsir al-Jalalayn, commentary on 51:5, via Quran.com. The reader has the full commentary and 9 more tafsirs.