The first Caliph of Muslims
8-7-2002 | IslamWeb
Question:
Who is the Caliph of the Muslims, Abu Bakr or ‘Ali, may Allaah be pleased with them both?
Answer:
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 doubt that the best person among the Muslims after the Prophet, sallallaahu ‘alayhi wa sallam, is Abu Bakr As-Siddeeq, then 'Umar ibn Al-Khattaab, then ‘Uthmaan ibn ‘Affaan, and then ‘Ali ibn Abi Taalib 
.
As for the position of Khilaafah (Caliphate) after Allaah's Messenger, sallallaahu ‘alayhi wa sallam, they succeeded one another as follows: Abu Bakr, 'Umar, ‘Uthmaan and then 'Ali all. Shaykhul-Islam Ibn Taymiyyah 
said, “Whoever impugns or argues about the rightness of the Khilaafah of the four rightly-guided Caliphs (Abu Bakr, 'Umar, ‘Uthmaan and 'Ali ) is in fact more astray than a donkey.”
Here is a narration that supports the above-stated points: Al-Bukhaari and others reported from 'Abdullaah ibn 'Umar both, who said, "We were asked about the best people during the time of the Prophet, sallallaahu ‘alayhi wa sallam, and we opted for Abu Bakr, then 'Umar and then ‘Uthmaan."
Al-Bukhaari reported from Muhammad ibn Al-Hanafiyyah, who said, "I asked my father (‘Ali), 'Who is the best one after Allaah's Messenger?' He said, ' Abu Bakr.’ I said, 'Who is the next?' He answered, ''Umar'. And I feared that he would say '’Uthmaan'. Then, I said, 'And you are the third.' He (‘Ali) replied, 'I am just a man from among the Muslims.'
‘Ali 
said the above narration during the period in which he was a Caliph, to indicate that he believed in the legitimacy of the Khilaafah of Abu Bakr .
In the same vein, the Prophet, sallallaahu ‘alayhi wa sallam, chose Abu Bakr to lead the Muslims in prayer. He, sallallaahu ‘alayhi wa sallam, said: "Order Abu Bakr to lead the Muslims in prayers." This is another piece of evidence that proves the legitimacy of Abu Bakr's Khilaafah. Then, it became natural to choose Abu Bakr a Caliph to lead the Muslims in their worldly affairs after becoming their leader in religion.
Based on Chapter Al-Faatihah, Al-Imam Ash-Shinqeeti produced a bright piece of evidence that proves the legitimacy of Abu Bakr's Khilaafah in his book 'Adwaa Al-Bayaan'; it is as follows: Allaah The Almighty Says (what means): {“The way of those on whom You have bestowed Your grace…”}[Quran 1:7] Ash-Shinqeeti said, “The clear meaning of the above-verse is clearly stated in Chapter 4 (An-Nisaa`): {And whoso obeys Allaah and the Messenger (Muhammad, sallallaahu ‘alayhi wa sallam), then they will be in the company of those on whom Allaah has bestowed His grace, of the Prophets, the Siddeeqoon (those followers of the Prophets who were first and foremost to believe in them, like Abu Bakr As-Siddeeq ), the martyrs, and the righteous. …}[Quran 4: 69] He added, “Abu Bakr is on the upright way since he is one of the Siddeeqoon. This means that his Khilaafah is right.”
As a final word, a Caliph of Muslims is the one who all Muslims or most of them agreed upon and accepted him as their leader. All these characteristics were certainly met by Abu Bakr, then ‘Umar, then ‘Uthmaan and then ‘Ali .
Allaah Knows best.