“You are in the sacred valley of Tuwa”: that is, the purified valley. Tuwa is the name of the valley. The scholars of Kufa and Syria recited Tuwa with nunation here and in Surah al-Nazi‘at, whereas the others recited it without nunation, because it is an altered form of Tawin. Since it has been altered from its original form, it is declined irregularly, like ‘Umar and Zufar. Al-Dahhak said: “Tuwa is a rounded, deep valley, like a well in its circular shape.”