Is it permissible to pay Zakat for one's parents, who do not pay it themselves despite being able to do so, while not wishing to give them the money directly for fear that they might spend it on things other than the rightful recipients of Zakat?

Zakat (definition) is a pillar and an obligation, and failing to pay it is among the major sins. It is obligatory to advise one's parents to pay it. Whoever has neglected to pay Zakat for years must repent and pay the Zakat for each year. Paying Zakat on behalf of someone without their authorization is not valid due to the absence of intention, but it is valid with their permission.