Ma'arif al-Qur'an
Mufti Muhammad ShafiCommentary
We have already seen that Sayyidna Zakariyya (علیہ السلام) believed in the absolute power of Allah and had seen its manifestation repeatedly and that he had himself made the prayer and knew of its acceptance as well, what then, did he mean by asking: 'how shall I have a boy?' The truth of the matter is that the question asked by him was not be-cause of any doubt in the absolute power of Allah. Quite contrary to this, the purpose of the question was to find out the state in which this was to happen: whether the present extreme old age of both of them would remain just as it was, or would that state be changed. The eloquent reply given in كَذَٰلِكَ اللَّـهُ يَفْعَلُ مَا يَشَاءُ (That is how Allah does what He wills) makes it clear that they were to remain at the same age and that they would have an offspring in that very state. This resolves any doubt that may be entertained at this point. (Bayn al-Qur'n)