Why didn't Muhammad, sallallaahu 'alayhi wa sallam, select a ruler (Khalifa) after him in his lifetime?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

There is no clear-cut text from the Prophet in which he appointed Abu Bakr as a leader after him, according to the correct position of the scholars . However, the Prophet gave the Muslims several indications which led them toward that direction. Moreover, the Prophet endorsed Abu Bakr and was even about to issue a decree about his caliphate, but when he knew that the Muslims would consent about his leadership he left the matter to them. 'Aa'ishah said, “When the Prophet was sick [during his death sickness] he said to me: "Call Abu Bakr and your brother to me, so that I would write a decree, as I fear that someone would say: ''I am more deserving than him, and Allaah and all the believers refuse anyone else but Abu Bakr." [Muslim]

As a matter of fact, the Prophet had chosen him to lead the people in prayer during the death sickness, and the Companions considered this an indication from him that Abu Bakr was his successor, as they said, "The Prophet has accepted him for our religion, then will we not accept him for our worldly affairs." This is reported by Ibn 'Abdul-Baar in his book 'At-Tamheed' from the narration of 'Ali and many scholars quoted this report.

The method of using this evidence as a proof for the qualification of Abu Bakr to lead the Muslims after the Prophet is called “Qiyaas Al-‘Awla” (Proving what is lower, by an analogy, on an evidence that proves what is higher)by the majority of the scholars of Usool .

The consensus of the believers on Abu Bakr’s leadership as a Caliph suffice us from needing a text in this connection.

Furthermore, there are many points of wisdom for not having a text from the Prophet appointing Abu Bakr . Among these points is the knowledge of the Prophet that the believers will not accept anyone other than Abu Bakr as a leader as mentioned in a narration reported by Muslim . In addition, in this (not writing) there is an affirmation for the right of the Muslims to choose their own leader and so forth.

For more benefit, please refer to Fatwa 84781.

Allaah Knows best.