If a Muslim dies without having performed the obligation of Hajj, and they satisfy all the conditions that make Hajj obligatory on them, it is obligatory to perform Hajj on their behalf with the money they left, whether they left a will stating this or not. If another person performs Hajj on behalf of the deceased, provided that it is valid for them to perform Hajj (satisfy the conditions of being Muslim, sane, adult), and have already performed Hajj for themselves, the Hajj they perform on behalf of the deceased will be valid and will sufficiently discharge the obligation on his part. As to whether the Hajj performed on behalf of someone else is equal to the Hajj performed for oneself, or more or less meritorious than it, this is up to Allah (Glorified be He). There is no doubt that those who are obligated to perform Hajj and have the ability for it should hasten and perform it before their death, as the evidence from the Shari‘ah (Islamic law) states this and it should be done to avoid the sin of delaying it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.