Tafsir of Ash-Shu`ara' 26:69

Ibrāhīm (peace be upon him) knew that they were idol-worshippers; however, he questioned them to demonstrate that what they worshipped possessed no merit for worship whatsoever.

It is like when you ask a merchant, "What is your wealth?" while you already know his wealth is slaves. Then you say to him, "Slaves are beauty, not wealth."

If you ask: "What do you worship?" is a question regarding the object of worship only. Therefore, the standard response should have been, "Idols," just as in the Almighty’s sayings: "They ask you about wine and gambling, say..." (2:219), "What has your Lord said? They said, 'The truth'" (34:23), and "What has your Lord sent down? They said, 'Good'" (16:30).

I reply: These people presented the story of their affair in its entirety, as if they were rejoicing in it and boasting of it. Thus, it included Ibrāhīm’s question and their intent to manifest the joy and pride within their souls. Do you not see how they appended to their statement "we worship" the phrase "and we remain devoted to them" (26:71), rather than limiting themselves to "we worship" alone?

An example of this is when you ask a rogue, "What do you wear in your land?" and he replies, "I wear the Atḥamī cloak, and I drag its hem among the maidens of the neighborhood."

They said "we remain" (naẓallu) because they worshipped them during the day, not the night.