What are the conditions and regulations for an illness that prevents one from performing Hajj?

The criterion for illnesses that prevent the obligation of Hajj is any disease that hinders travel or performance. If a person has an impediment that is not expected to cease (like a disabled person), possesses wealth, finds someone to perform Hajj on their behalf for a reasonable wage, and that person has already performed Hajj for themselves, then it is obligatory upon him to appoint someone else to perform it (inabah). This is the view of the majority of scholars, based on the Hadith of the Khath'amiyah woman. However, if the disabled person does not have wealth, or cannot find someone to perform Hajj on their behalf, or finds someone but at a cost exceeding the reasonable wage, then Hajj is no longer obligatory upon him.