أَهُمْ يَقْسِمُونَ رَحْمَتَ رَبِّكَ
Is it they who apportion your Lord’s mercy?
The pronoun hum follows the interrogative hamza and becomes the focus. The rhetorical denial challenges their authority as the agents who apportion divine mercy, not the existence of mercy itself.
This shows why identifying the fronted participant matters: the issue is whether the asserted actor has the relevant authority, not merely whether any apportionment occurs.