قَدْ أَفْلَحَ مَنْ زَكَّاهَا وَقَدْ خَابَ مَنْ دَسَّاهَا
Successful indeed is whoever purifies it, and disappointed is whoever corrupts it. (91:9–10)
On the common classical analysis, qad aflaha is the answer of the extended oath. Qad with the past form reinforces realized certainty. Other exegetes take the oath response as omitted and regard this clause as a related independent assertion.
A sound lesson explains the dominant reading while acknowledging the documented alternative. Qad here is neither a future marker nor a negation particle.