al-Qamar 54:23

Kadhdhabat Thamūdu bi'l-nudhur "Thamūd denied the warnings."

In the two preceding accounts the verb had no object: kadhdhabat ʿĀdun — "ʿĀd denied", simply. Here there is an object: bi'l-nudhur.

And this object will be repeated in the remaining two accounts as well:

There is an intensification in the sequence, and I record it as my own reading. In the first two accounts the verb has no object — the denying is set down absolutely. In the third and fourth the object is nudhur. In the fifth the object is āyātinā kullihā — "all Our signs". The scope of the denying, that is, widens as the list advances.

A note on the particle بِ: in the Qurʾān the verb kadhdhaba takes both a direct object (kadhdhabū rusulanā) and a bi-object (kadhdhabū bi-āyātinā). When it comes with bi, the object is mostly a thing (a sign, a book, the Hour, the religion); when it comes directly, mostly a person (a messenger, a prophet). I draw attention to this distribution but do not present it as a rule; it may have exceptions.

If the distribution holds, then in the expression bi'l-nudhur the sense "warnings" (a thing) comes forward and the sense "warners" (persons) stays in the background. This is an inclination, not a ruling.