On other occasions, the Prophet himself asked questions. Sura 19: 64 was revealed in response to such a question by the Prophet Muhammad:

Narrated Ibn 'Abbas: The Prophet said to the Angel Gabriel, What prevents you from visiting us more often than you visit us now? So there was revealed: 'And we (angels) descend not but by the command of your Lord. To Him belongs what is before us and what is behind us ...' (19: 64).' [Bukhari, VI, No. 255.]