Surah Al-Mu'minun 23:77

حَتَّىٰٓ إِذَا فَتَحْنَا عَلَيْهِم بَابًا ذَا عَذَابٍ شَدِيدٍ إِذَا هُمْ فِيهِ مُبْلِسُونَ

Until when We have opened before them a door of severe punishment, immediately they will be therein in despair.

Translation: Saheeh International

Tafsir

Until hattā is for inceptiveness when We opened on them the gate of a severe chastisement namely the day of Badr slaying them behold! they are aghast thereat despairing of anything good.

Excerpt from Tafsir al-Jalalayn, commentary on 23:77, via Quran.com. The reader has the full commentary and 9 more tafsirs.