What happens if parents permit Jihad on the condition that their son does not fight, and he participates in combat?

Primary text

If his parents permitted him to engage in raiding (Ghazw) but stipulated that he must not fight, and he participates in the fighting, the Jihad becomes obligatory upon him, and their condition is nullified. Al-Awza'i and Ibn al-Mundhir hold this view because the action has become obligatory upon him, leaving no room for obedience to them in abandoning it.