It is narrated from Sayyiduna Abu Mahdhurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) ordered about twenty men to call the adhan. They gave the adhan, and the Prophet (peace and blessings be upon him) liked the voice of Sayyiduna Abu Mahdhurah (may Allah be pleased with him), so he taught him the adhan: « اللهُأَكْبَرُ،اللهُأَكْبَرُ ، اللهُأَكْبَرُ،اللهُأَكْبَرُ » "Allah is the Greatest, Allah is the Greatest, Allah is the Greatest, Allah is the Greatest" « أَشْهَدُأَنْلَاإِلَهَإِلَّااللهُ،أَشْهَدُأَنْلَاإِلَهَإِلَّااللهُ، » "I bear witness that there is no deity worthy of worship except Allah, I bear witness that there is no deity worthy of worship except Allah" « أَشْهَدُأَنْمُحَمَّدٌرَسُولُٱللَّٰه ، أَشْهَدُأَنْمُحَمَّدٌرَسُولُٱللَّٰه » "I bear witness that Muhammad is the Messenger of Allah, I bear witness that Muhammad is the Messenger of Allah" « حَيَّعَلَىالصَّلَاةِ،حَيَّعَلَىالصَّلَاةِ » "Come to prayer, come to prayer" « حَيَّعَلَىالْفَلَاحِ،حَيَّعَلَىالْفَلَاحِ » "Come to success, come to success" « اللهُأَكْبَرُ،اللهُأَكْبَرُ » (Allah is the Greatest, Allah is the Greatest) « لَاإِلَهَإِلَّااللهُ » "There is no deity worthy of worship except Allah" and the Prophet (peace and blessings be upon him) taught him to say the iqamah in a doubled manner.
This is of the category of permissible differences. It is permissible for the muezzin to recite the tarji‘ in the adhan and to say the iqamah in a doubled manner, and it is also permissible to say the adhan in a doubled manner and the iqamah in a single manner. Because both actions are established from the Prophet Muhammad (peace be upon him), but a doubled adhan and a doubled iqamah together are not established from the Prophet Muhammad (peace be upon him).