How do we answer someone who asks why Allah permitted the killing and crucifixion of Ibn Az-Zubayr?

Ibn Al-Zubayr was not unique among the righteous who were tested in the way of Allah. Affliction descends upon prophets and the righteous for a divine wisdom, and as a mark of honor and an elevated status for them. His mother Asma endured his death, recalling that the head of John (Yahya), peace be upon him, was presented to a harlot. Thus, what happened to Ibn Al-Zubayr was for his honor with Allah and an humiliation for his enemy. The most severely tested people are the prophets, then the next best, and so on. A person is tested according to his faith. Allah tests His servants to distinguish the truthful from the liar, and He honors some of them with what He has prepared for them in the Hereafter, for this world is worth nothing to Allah. And Allah is All-Knowing, All-Wise; He is not questioned about what He does.