Muhammad 47:21

TaAAatun waqawlun maAAroofun fa-ithaAAazama al-amru falaw sadaqoo Allaha lakanakhayran lahum

Obedience and good words. And when the matter [of fighting] was determined, if they had been true to Allāh, it would have been better for them.

The (reality of their) obedience and (truthfulness of their) speech is fully known (as being mere deception). So, had they been truthful to Allah when the matter had become serious, it would have been much better for them.