he would appoint a deputy. Whenever he performed Hajj or Umrah, he would likewise appoint one. Accordingly, he appointed deputies during the campaigns of Badr, Banū al-Mustaliq, Khaybar, and the Conquest of Mecca; during the campaigns of al-Hudaybiyyah and al-Qadā'; during the Farewell Hajj; and on other occasions.
Appointing a deputy during one’s lifetime is obligatory for the person vested with authority, even if he is not a prophet. Yet he is not required to appoint a successor after * his death: appointment during life is indispensable and the obligation cannot be discharged without it, unlike appointment after * (1) death. For the Prophet has already conveyed the message to the Ummah, and it is he whom they must obey after his death; they themselves can appoint someone to exercise authority over them, just as may be done with every communal obligation requiring a particular individual. It is therefore evident that the obligation to appoint a deputy during one’s lifetime does not entail an obligation to appoint a successor after death.
Fourth:
The appointment of deputies during one’s lifetime is obligatory in the various spheres of authority. Thus, the Prophet (may Allah bless him and grant him peace) would appoint over people from whom he was absent (2) someone to discharge the required duties among them. He would appoint deputies to oversee the Hajj, collect zakat, safeguard the fay' revenues, enforce the prescribed legal penalties, lead military expeditions, and perform other functions.
It is well known, by the agreement of all rational people, that this type of appointment is not obligatory after death; indeed, it is not even possible. It is impossible to designate for the Ummah, after his death, someone to take charge of every individual matter, for they will need one person after another, and designating all of them is impossible. Furthermore, even if he designated one individual, that person’s circumstances might change and he might have to be dismissed. During his lifetime, the Prophet would appoint officials and then, when someone complained (3) to him about an official, dismiss him—as he dismissed al-Walīd ibn Uqbah and dismissed Sa'd (4) ibn Ubādah