Tafsir of Al-Qamar 54:31

(Indeed, We sent upon them a single cry) — which is the cry of Gabriel, peace be upon him; he shouted on the morning of Sunday, as Al-Manawi narrated from Al-Zamakhshari — (at the side of their dwellings).

(So they became) — meaning, they turned into — (like the dry twigs of the pen-builder). That is, like the withered plants that the owner of a pen gathers for his livestock in winter. In Al-Bahr, it is stated that hashim (dry twigs) refers to what has crumbled and broken from trees. The muhtazir is the one who constructs a hazirah (pen/enclosure), from which parts crumble and fall off during the process of construction. Alternatively, hashim may refer to that which has dried up within the enclosure over a long period, which the livestock then tread upon, causing it to crumble. This view is challenged by the position that the more apparent meaning is "like the dry twigs of the enclosure."

The hazirah is the fold or shelter that the Arabs and desert dwellers construct for livestock and habitation, made from branches, leafy trees, and reeds, derived from al-hazr, meaning "to prevent" or "to restrain."

Abu Haywah, Abu al-Samal, Abu Raja, and Amr ibn Ubayd read al-muhtazar with a fatha on the za, as a noun of place, with the intended meaning being the enclosure itself. It may also be a passive participle. It is said: a noun is implied for it, meaning "like the dry twigs of the [wall/fence] that is enclosed," or it is not implied, on the basis that al-muhtazar is the pen itself, as you have heard. It is also permissible for it to be an infinitive, meaning "like the dry twigs of constructing the pen," that is, what crumbles during the process of construction.