Praise be to Allaah.  

Several versions of the adhaan have been narrated in sound reports from the Prophet (peace and blessings of Allaah be upon him). It is Sunnah to use all the versions that have been narrated from him in order to revive the Sunnah and to put an end to disputes and differences that may be raised by those who have no knowledge or who are fanatical about their own madhhabs. 

Shaykh Ibn ‘Uthaymeen said: 

Everything that has been narrated in the Sunnah about the adhaan is permissible. Rather what should be done is to recite one version sometimes and another version sometimes, so long as that will not cause confusion and fitnah (tribulation). 

Maalik narrated seventeen phrases to be recited, starting with Allaahu akbar, to be said twice; then the muezzin should recite the Shahaadatayn to himself first, then say them out loud and continue with the adhaan. 

According to al-Shaafa’i, there are nineteen phrases with the takbeer at the beginning four times; then the muezzin should recite the Shahaadatayn to himself first, then say them out loud and continue with the adhaan. 

All of this was narrated in the Sunnah, so if you give the call to prayer one way sometimes and in the other way sometimes, this is better. The basic principle is that in the case of acts of worship which were narrated in different ways, it is preferable to do them in all of those ways. 

Al-Sharh al-Mumti’, 2/51, 52 

The madhhab of Imam Ahmad and Abu Haneefah is that the adhaan consists of fifteen phrases; this is the adhaan of Bilaal (may Allaah be pleased with him). 

The evidence for the view of Maalik and al-Shaafa’i: 

It was narrated from Abu Mahdhoorah that the Prophet of Allaah (peace and blessings of Allaah be upon him) taught him this adhaan:

Allaahu akbar, Allaah akbar, ash-hadu an laa ilaah ill-Allaah, ash-hadu an laa ilaah ill-Allaah, ash-hadu anna Muhammadan rasool-Allaah, ash-hadu anna Muhammadan rasool-Allaah. Then he should repeat, ash-hadu an laa ilaah ill-Allaah, ash-hadu an laa ilaah ill-Allaah, ash-hadu anna Muhammadan rasool-Allaah, ash-hadu anna Muhammadan rasool-Allaah. Hayya ‘ala al-salaah – twice; hayya ‘ala’l-falaah – twice; Allaahu akbar, Allaahu akbar, Laa ilaaha ill-Allaah. 

Narrated by Muslim, 379. 

This hadeeth is the evidence quoted for the view of Maalik and al-Shaafa’i, because it describes two ways of reciting the takbeer at the beginning of the adhaan – twice according to the view of Maalik and four times according to the view of al-Shaafa’i. 

Al-Nawawi (may Allaah have mercy on him) said: 

This hadeeth in Saheeh Muslim also mentions saying Allaahu akbar only two times at the beginning. Elsewhere than in Muslim it says that Allaah akbar should be said four times. Al-Qaadi ‘Iyaad (may Allaah have mercy on him) said: in some reports in Saheeh Muslim it mentions saying it four times. Al-Shaafa’i, Abu Haneefah, Ahmad and the majority of scholars said that it is to be repeated four times, and Maalik said that it is to be repeated twice, and he quoted this hadeeth as evidence. 

The evidence for the view of Abu Haneefah and Ahmad: 

It was narrated that ‘Abd-Allaah ibn Zayd said: When the Messenger of Allaah (peace and blessings of Allaah be upon him) ordered that a bell should be made so that it could be struck to call the people to prayer, a man walked around me whilst I was sleeping [i.e., in a dream], carrying a bell in his hand. I said, “O slave of Allaah, will you sell this bell?” He asked, “What will you do with it?” I said, “We will call the people to prayer.” He said, “Shall I not tell you of something better than that?” I said, “Yes.” He said, “Say: Allaahu akbar, Allaah akbar, Allaahu akbar, Allaah akbar; ash-hadu an laa ilaah ill-Allaah, ash-hadu an laa ilaah ill-Allaah; ash-hadu anna Muhammadan rasool-Allaah, ash-hadu anna Muhammadan rasool-Allaah; hayya ‘ala al-salaah, hayya ‘ala al-salaah; hayya ‘ala’l-falaah, hayya ‘ala’l-falaah; Allaahu akbar, Allaahu akbar; Laa ilaaha ill-Allaah

(Allaah is most Great, Allaah is most Great, Allaah is most Great, Allaah is most Great. I bear witness that there is no god except Allaah, I bear witness that there is no god except Allaah. I bear witness that Muhammad is the Messenger of Allaah, I bear witness that Muhammad is the Messenger of Allaah. Come to prayer, come to prayer; come to success, come to success. Allaah is most Great, Allaah is most Great, there is no god except Allaah).” Then he went a short distance away from me and said: “And when the prayer is about to begin (iqaamah), say:

Allaahu akbar, Allaah akbar; ash-hadu an laa ilaah ill-Allaah; ash-hadu anna Muhammadan rasool-Allaah; hayya ‘ala al-salaah, hayya ‘ala’l-falaah; qad qaamat il-salaah, qad qaamat il-salaah (prayer is about to begin); Allaahu akbar, Allaahu akbar; Laa ilaaha ill-Allaah

The following morning, I went to the Messenger of Allaah (peace and blessings of Allaah be upon him) and told him what I had seen. He said, “This is a true dream, in sha Allah. Get up with Bilaal and teach him what you saw, for he has a more melodious voice than you.” So I got up with Bilaal and taught him, and he gave the call to prayer. ‘Umar ibn al-Khattaab heard that in his house and he came out, dragging his lower garment and saying, “By the One Who sent you with the truth, O Messenger of Allaah, I saw the same as he saw!” The Messenger of Allaah (peace and blessings of Allaah be upon him) said, “To Allaah be praise.” 

Narrated by Abu Dawood, 499; classed as saheeh by Ibn Khuzaymah, 1/191 and Ibn Hibbaan, 4/572. al-Tirmidhi narrated that Imam al-Bukhaari deemed it saheeh, as it says in Sunan al-Bayhaqi, 1/390. 

Shaykh al-Islam Ibn Taymiyah said: 

As this is the case, the correct view is the view of Ahl al-Hadeeth and those who agree with them, which is to accept everything that has been narrated from the Prophet (peace and blessings of Allaah be upon him) and not to disapprove of any of these narrations, because the variations in the adhaan and iqaamah are like the variations in the recitation and tashahhud etc.… No one has the right to disapprove of anything that the Messenger of Allaah (peace and blessings of Allaah be upon him) has prescribed for his ummah. With regard to those who dispute and are divided on such issues, to the extent that they regard people as friends or enemies, or fight over such issues in which variation is approved of by Allaah, as some of the people in the east do, they are among those who split up their religion (i.e. who left the true Islamic Monotheism), and became sects, [i.e. they invented new things in the religion (Bid‘ah), and followed their vain desires]  [cf. al-Room 30:32]. In order to follow the Sunnah completely we should do it one way one time and the other way another time, this way in one place and the other way in another place, because forsaking what was narrated in the Sunnah and adhering to something else may lead to regarding what is Sunnah as bid’ah and regarding something that is mustahabb as obligatory, and that would lead to division and disputes if others do it the other way. So the Muslim should pay attention to the general principles which call for adherence to the Sunnah and the jamaa’ah (main body of Muslims), especially with regard to prayers in congregation.  Saying the Shahaadatayn twice in a low voice and then repeating that out loud in the was the option favoured by Maalik and al-Shaafa’i, but Maalik thought that the takbeer should be said twice and al-Shaafa’i thought that it should be said four times, whereas Abu Haneefah thought that the Shaahadatayn should not be said in a low voice during the adhaan. With regard to Ahmad, he said that both ways were Sunnah but he preferred not to do it, because that was the adhaan of Bilaal. 

With regard to the iqaamah, Maalik, al-Shaafa’i and Ahmad said that the phrases should be said once, but Ahmad said that saying them twice is Sunnah. All three of them, Abu Haneefah, al-Shaafa’i and Ahmad, preferred to say Qad qaamat il-salaah twice, whereas Maalik did not. And Allaah knows best. 

Majmoo’ al-Fataawa, 22/66-69 

And Allaah knows best.