The Islamic Personality by Sheikh Taqīuddīn An-Nabahānī

The Khilafah is not contracted by appointing a successor or heir, because it is a contract between the Muslims and the Khalifah. The pledge by the Muslims and the acceptance from the person whom they elect is a condition in the contract of the Khilafah. The appointment of a successor or heir does not suit to include this condition, so the Khilafah is not established with it. Accordingly, the appointment of the next Khalifah, by the existing Khalifah, is not included in the Khilafah contract because he does not have the right to contract it, and because the Khilafah is a right of the Muslims, not the Khalifah, and they contract it to whom they wish. So the appointment of the next Khalifah or recommending him by the existing Khalifah is not correct, because he gives something which he does not possess. Giving something which is not possessed by the giver is illegal. So the existing Khalifah cannot appoint another Khalifah to succeed him, whether he was his son or relative or a person remote to him, and the Khilafah is not contracted to him at all because its contract was not carried out by those who have it. Thus it is a redundant (fudhuli) contract.

As for what was narrated that Abu Bakr (ra) appointed ‘Umar (ra), and ‘Umar (ra) appointed the six persons from the Sahabah (ra), and that the Sahabah had agreed on that and they did not challenge this action and thus it was an Ijma’a from them; this does not indicate that the appointment of a successor is legal. This is because Abu Bakr (ra) did not appoint a Khalifah, rather he consulted the Muslims about who might be the Khalifah for them and he nominated ‘Ali (ra) and ‘Umar (ra). Then the Muslims in three months during the life of Abu Bakr (ra), chose ‘Umar (ra) by their majority. Then after the death of Abu Bakr (ra), the people came and gave their pledge to ‘Umar (ra), and hence the Khilafah was contracted to ‘Umar (ra). But before the pledge ‘Umar (ra) was not a Khalifah and the Khilafah was not established to him, neither by the nomination of Abu Bakr (ra) nor by his selection by the Muslims. It was rather contracted when they gave him their pledge and he accepted it. As for the appointment of the six people by ‘Umar (ra), it was a nomination to them by him upon the request of the Muslims. Then ‘Abdurrahman bin ‘Auf (ra) consulted the Muslims about whom they wanted from the six people. The majority wanted ‘Ali (ra) if he adhered to the practices of Abu Bakr (ra) and ‘Umar (ra), otherwise they wanted ‘Uthman (ra). When ‘Ali (ra) rejected to adhere to the practices of Abu Bakr (ra) and ‘Umar (ra), ‘Abdurrahman bin ‘Auf (ra) gave the pledge to ‘Uthman (ra) and the people gave their pledge. So the Khilafah was contracted to ‘Uthman (ra) by the pledge given to him by the people, not by the nomination of ‘Umar (ra) or the selection of the people. Had not the people given him their pledge, the Khilafah would not have been contracted to him. Therefore, there must be a pledge by the Muslims to the Khalifah, and it is not allowed to occur by appointing a successor or an heir, because the bay’ah is a contract of ruling and the Shari’ah law of contract applies to it