Surah Al-Qalam 68:42

يَوْمَ يُكْشَفُ عَن سَاقٍ وَيُدْعَوْنَ إِلَى ٱلسُّجُودِ فَلَا يَسْتَطِيعُونَ

The Day the shin will be uncovered and they are invited to prostration but they [i.e., the disbelievers] will not be able,

Translation: Saheeh International

Tafsir

Mention the day when the shank is bared an expression denoting the severity of the predicament during the reckoning and the requital on the Day of Resurrection one says kashafati’l-harbu ‘an sāqin ‘the war has bared its shank’ to mean that it has intensified and they are summoned to prostrate themselves as a test of …

Excerpt from Tafsir al-Jalalayn, commentary on 68:42, via Quran.com. The reader has the full commentary and 9 more tafsirs.