When prayer is not required in a recognized case, the Wudu required for that prayer is not required either. The example is a woman during menstruation1: the prayer obligation and its Wudu obligation do not apply then.
There is also a distinction concerning reward. If a person performs Wudu but does not then pray, its goodness and reward are diminished in this explanation of the relationship.
“Diminished” is not the same as “no reward at all,” nor does it mean that the Wudu did not occur. The point is the connection between the preparation and its purpose.
1. Menstruation: the monthly bleeding period, used here as the stated example of prayer not being required.
- The Effect of That Dependence