What is the ruling on deputizing for the pillars and obligations of Hajj?

If a person is unable to perform Hajj himself due to old age or an incurable illness, yet possesses the financial means, then, according to the majority of scholars, it is obligatory for him to appoint someone to perform Hajj on his behalf, based on the hadith (definition) of Ibn Abbas. As for one who is able to perform Hajj himself, it is unanimously impermissible for him to appoint a proxy for the obligatory Hajj. If throwing the pebbles (ramy al-jimār) becomes difficult for someone due to illness or old age, he is permitted to appoint a proxy for it. However, circumambulation (tawāf), striving (sa'y), standing at Arafat (wuqūf bi-Arafah), and staying overnight in Muzdalifah (mabīt bi-Muzdalifah) cannot be performed by proxy; rather, the pilgrim must perform them himself. The weak are permitted to depart from Muzdalifah after midnight. If someone is unable to stay overnight in Mina, there is no obligation upon him. Hajj is invalid if any of its pillars are missing: ihram (definition), standing at Arafat, tawaf (definition), and sa'y. It is permissible for the pilgrim to appoint someone else to slaughter the sacrificial animal (hady).