Tafsir of Al-Jinn 72:5

This is an apology on their part for having followed their fool. That is to say: We used to think that no one would lie about Allah the Exalted by attributing to Him, Glorified be He, a consort or a child. Therefore, we believed in the validity of the fool's statement.

Perhaps the [act of] belief relates to what their words imply and naturally lead to regarding their error in that assumption; as if it were said: "And we believed in our error regarding the assumption because of which we believed what we believed."

Kadhiban (a lie) is a verbal noun (masdar) emphasizing taqula (to say), because it is a type of saying—similar to the phrase "I sat in the qurfusa' (squatting) position"—or it is an adjective for a deleted verbal noun, meaning "a false saying," i.e., fabricated. This is because it is inconceivable that a lie could emanate from Him, even if it is famously described as such, like the one who says [otherwise].

It is also permitted that it is a case of describing with the verbal noun by way of hyperbole, and the [emphasis] returns to the negation, not the negated [verb].

Al-Hasan, al-Jahdari, 'Abd al-Rahman ibn Abi Bakra, Ya'qub, and Ibn Miqsam read the present tense tataqawwala (to fabricate), and its origin is tataqawwala with two tas, one of which was elided. Thus, kadhiban acts as an emphasizing verbal noun, because a lie is [by definition] fabrication.