Surah Al-Mursalat 77:12
لِأَىِّ يَوْمٍ أُجِّلَتْ
For what Day was it postponed?
Translation: Saheeh International
Tafsir
For what day — for a tremendous day — has it been appointed? it has been appointed for witnessing of the messengers against their communities to the effect that they delivered their messages from God.
Excerpt from Tafsir al-Jalalayn, commentary on 77:12, via Quran.com. The reader has the full commentary and 9 more tafsirs.