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.
It is not an obligation that the Iqaamah (the call that is made immediately prior to commencing the prayer) be called by the person who called the Athaan (call for the prayer), but this is something desirable according to the view of many scholars .
Ibn Qudaamah from the Hanbali School of jurisprudence, said in his book entitled “Al-Mughni”: “The person who calls the Athaan should call the Iqaamah, this is also the view of Imaam Ash-Shaafi’i, while Imaam Abu Haneefah and Imaam Maalik said that there is no difference between him and others in this regard; ... We have as evidence the saying of the Prophet in the Hadeeth narrated by Ziyaad Ibn Al-Haarith As-Sudaa’i that “the brother from Sudaa’ (a name of a tribe) made the Athaan, and whoever calls the Athaan, should call the Iqaamah”, and because they are two acts of the mention of Allaah that are said before the prayer, so it is a Sunnah that they both be done by the same person, (exactly) like the two Khutbas of the Friday prayer….”
Therefore, it is not desirable for a person other than the one who called the Athaan to call the Iqaamah; “Kashshaaf Al-Qinaa’”, a Hanbali book, reads: “It is not desirable for a person other than the one who called the Athaan to call the Iqaamah….”
In case of dispute, the person who called the Athaan should call the Iqaamah pursuant to the Sunnah and as a way of putting an end to disagreement and dispute unless the Athaan was called by a group of people [for example, in the past, when the mosque was very big, one person would call the Athaan on one side of the mosque and another person would call it on another side of the mosque and so forth] and then there is a dispute between them (i.e. the persons who called the Athaan) over the one who is more entitled to call the Iqaamah, then in this case drawing lots should be done between them. Ash-Shawkaani said in his book entitled “Nayl Al-Awtaar”: “If it is only one person who called the Athaan, then it is him who should call the Iqaamah and if it is a group of people who called the Athaan at the same time, and they agree on someone among them to call the Iqaamah, then such a person should call the Iqaamah, and if they disagree, they should draw lots….”
However, the person who called the Athaan should be kind and gentle in demanding his right to call the Iqaamah. Whenever kindness is added to something, it adorns it and whenever it is withdrawn from something, it leaves it defective.
Indeed, uniting the hearts of Muslims is something Islamically required. Hence, if this person who has the right to call the Iqaamah [because he called the Athaan] leaves it to the other one who has commenced calling the Iqaamah in order to gain over the hearts of Muslims and uniting them, then it is hoped that he will be rewarded for doing so, Allaah willing.
Allaah Knows best.