والوضوء حسن بواسطة كونه مفتاحا للصلاة
Ablution is good in this respect because it is a means to the ritual purity required for prayer.
When a prayer requires purity for its valid performance, ablution may serve as the necessary preliminary act. The particular obligation to obtain ablution is linked to the required prayer and its condition of purity.
Where the relevant prayer duty is absent, one cannot infer this specific obligatory ablution from that prayer alone. Voluntary ablution and its other legitimate uses are separate issues. One must distinguish the instrumental requirement from the underlying act of worship.