Reference: Silsilah Fataawa Noor ‘alad-Darb – Tape 6
Question: Who is responsible for [performing] hajj on behalf of the father & mother, if they are still alive, but are not able to perform hajj?
Response: No one is responsible [for performing hajj] on their behalf. Indeed, acts of worship are [only] obligatory upon the individual responsible, and not other than him; and if an act of worship of a person was made obligatory upon another [to perform], then this would certainly entail sin if he left it. And Allaah Ta’aala said:
And if both parents are unable to perform [their] hajj themselves – despite having the [necessary] funds, then one of their children can perform hajj [each] on their behalf. And if they were both able to physically perform hajj, then it is not permissible for anyone to perform the obligatory hajj [each] on their behalf; [however], there is no harm in [performing] the voluntary [hajj each on their behalf].