Affirmative imperfect used circumstantially

Supplementary Practice 15: Caravan Reports, Attribution and the Limits of Inference

دَخَلَ الرَّسُولُ يَبْتَسِمُ.
The messenger entered smiling.

Yabtassimu is an affirmative imperfect verbal clause functioning here as ḥāl without an introductory circumstantial wāw. It depicts an action or state occurring with the main event.

دَخَلَ الرَّسُولُ وَهُوَ يَبْتَسِمُ.
The messenger entered while he was smiling.

In the second version, wa-huwa initiates a nominal circumstantial sentence. It therefore does not contradict the rule governing a directly introduced affirmative imperfect circumstantial clause.