Surah Al-Anbya 21:38

وَيَقُولُونَ مَتَىٰ هَـٰذَا ٱلْوَعْدُ إِن كُنتُمْ صَـٰدِقِينَ

And they say, "When is this promise, if you should be truthful?"

Translation: Saheeh International

Tafsir

And they say ‘When will this promise of resurrection be fulfilled if you are truthful?’ about it.

Excerpt from Tafsir al-Jalalayn, commentary on 21:38, via Quran.com. The reader has the full commentary and 9 more tafsirs.