Shaykh Ibn Baaz (may Allaah have mercy on him) was asked: is it permissible to recite the iqaamah with the same number of phrases as the adhaan?
He said:
That is permissible, rather that is one of the Sunnahs in pronouncing the adhaan, because that was proven in al-Saheeh, from the hadeeth of Abu Mahdhoorah (may Allaah be pleased with him), when the Prophet (peace and blessings of Allaah be upon him) taught him the adhaan and iqaamah in al-Masjid al-Haraam at the time of the Conquest of Makkah.
It is permissible to mention the phrases of the iqaamah once only, apart from the phrase Qad qaamat il-salaah (prayer is about to begin) and the takbeer (Allaahu akbar), as Bilaal (may Allaah be pleased with him) used to do in the Mosque of the Prophet (peace and blessings of Allaah be upon him), in his presence and and according to his instructions. It is narrated in al-Saheehayn that Anas (may Allaah be pleased with him) said: Bilaal used to say the phrases of the adhaan twice and say the phrases of the iqaamah once in the presence of the Prophet (peace and blessings of Allaah be upon him).
Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah, 10/366
But in the case of acts of worship for which several ways of doing them have been narrated, it is better for the Muslim not to adhere to one particular way and ignore the rest. Rather the Sunnah is to do everything that has been proven from the Prophet (peace and blessings of Allaah be upon him). So one time he can say the iqaamah of Bilaal (may Allaah be pleased with him), and another time he can say the iqaamah of Abu Mahdhoorah (may Allaah be pleased with him).
Shaykh al-Islam Ibn Taymiyah (may Allaah be pleased with him) said:
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.
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.
Al-Fataawa al-Kubra, 2/43-44.