Surah Al-Muzzammil 73:14

يَوْمَ تَرْجُفُ ٱلْأَرْضُ وَٱلْجِبَالُ وَكَانَتِ ٱلْجِبَالُ كَثِيبًا مَّهِيلًا

On the Day the earth and the mountains will convulse and the mountains will become a heap of sand pouring down.

Translation: Saheeh International

Tafsir

on the day when the earth and the mountains will quake and the mountains will be like heaps of shifting sand mahīl derives from hāla yahīlu; it is actually mahyūl but the damma sound is considered too heavy for the yā’ and is therefore transposed onto the hā’ while the wāw the second of two unvocalised consonants is …

Excerpt from Tafsir al-Jalalayn, commentary on 73:14, via Quran.com. The reader has the full commentary and 9 more tafsirs.