فَذَكِّرْ إِنْ نَفَعَتِ الذِّكْرَىٰ
So remind, if the reminder benefits. (87:9)
“So remind” is an imperative linked to the preceding assurances. “If the reminder benefits” supplies a condition whose interpretation has been discussed in tafsīr; it foregrounds the benefit of admonition.
The mere presence of in does not justify a sweeping claim that every unsuccessful reminder is prohibited. Context and rhetorical purpose are essential. The initial fāʾ also signals a transition from promised aid to the task of reminding.