Why are there two adhaans for Jumu‘ah?
Question

                Why are there two adhaans for Jumu‘ah, although when the Prophet (blessings and peace of Allah be upon him) ascended the minbar only one adhaan was given in his presence?
Praise be to Allah.and blessings and peace of Allah be upon 
      the Messenger of Allah and upon his family and companions and those who 
      follow his guidance. To proceed: 
    
    Yes, it is as the questioner says. At the time of the Prophet 
    (blessings and peace of Allah be upon him), there was one adhaan, with the 
    iqaamah. When the Prophet (blessings and peace of Allah be upon him) came 
    out to deliver the khutbah and lead the prayer, the mu’adhdhin gave the 
    adhaan, then the Prophet (blessings and peace of Allah be upon him) 
    delivered the two khutbahs, then the iqaamah would be given. This is what is 
    known and this is what is narrated in the books of Sunnah, as the questioner 
    says, and it is something well-known to people of knowledge and faith. 

    But then the people’s numbers in Madinah increased at the 
    time of the Rightly Guided Caliph ‘Uthmaan ibn ‘Affaan (may Allah be pleased 
    with him), so he decided to add the third adhaan. It is called the first 
    adhaan, and is given to alert the people to the fact that this day is 
    Friday, so that they may prepare themselves and hasten to the prayer before 
    the regular adhaan that is given after the sun has passed the meridian. The 
    Sahaabah followed him in that at his time, such as ‘Ali (may Allah be 
    pleased with him), ‘Abd ar-Rahmaan ibn ‘Awf, one of the ten (who were 
    promised Paradise), az-Zubayr ibn al-‘Awwaam, who was also one of the ten, 
    Talhah ibn ‘Ubaydullah, and other senior Sahaabah. And this is how the 
    Muslims started to do it in most regions, following the action of the 
    Rightly Guided Caliph, ‘Uthmaan ibn ‘Affaan (may Allah be pleased with him); 
    he was followed in that by the Rightly Guided Caliph ‘Ali (may Allah be 
    pleased with him) and the rest of the Sahaabah. 

    The point is that this happened during the caliphate of 
    ‘Uthmaan and subsequently, and it has remained the practice of most of the 
    Muslims throughout the regions and throughout the centuries until the 
    present day, following the precedent that was set by ‘Uthmaan (may Allah be 
    pleased with him), on the basis of his ijtihaad and sincerity towards the 
    Muslims. And there is nothing wrong with that, because the Messenger 
    (blessings and peace of Allah be upon him) said: “I urge you to adhere to my 
    Sunnah and the way of the Rightly Guided Caliphs; hold fast to it.” He 
    (‘Uthmaan) was one of the Rightly Guided Caliphs, and the interest served by 
    that is quite clear. Hence this was adopted by Ahl as-Sunnah wa’l-Jamaa‘ah, 
    and they did not see anything wrong with it, because it was part of the 
    practice of the Rightly Guided Caliphs ‘Uthmaan and ‘Ali and those of the 
    Sahaabah who were present at that time (may Allah be pleased with them all). 
    End quote. 

    Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him)