Tafsir of Al-A'raf 7:121

(They said) is an initiation of a new sentence. Abu al-Baqa’ permitted it to be a circumstantial qualifier (hal) for the pronoun in "they turned back," but this is baseless. It has also been said: it is a circumstantial qualifier for the magicians, or for their hidden pronoun in "prostrating"—meaning they fell down prostrating while saying: (We have believed in the Lord of the worlds), meaning the Owner of their affairs and the One who disposes of them.