According to Ahnaf each words of iqamah are called two times. The people of India etc follow the same. And as per the other Imams each word of iqamah is called once except takbir and qad qamat as-salah, which is followed by the people of Arab etc. The proofs of Ahnaf are as follows:
عن عبدالله بن زيد قال : كان أذان رسول الله صلى الله عليه وسلم شفعاً شفعاً فى الأذان والإقامة .
Hadhrat Abdullah ibn Zaid (رضى الله عنه) says: The azan of the holy Prophet Muhammad (صلى الله عليه وسلم) contained 2-2 words and this was the case with iqamah. (Tirmidhi) In another hadith it is mentioned:
عن أبى محذورة أن النبى صلى الله عليه وسلم علمه الأذان تسع عشرة كلمة والإقامة سبع عشرة كلمة .
Hadhrat Abu Mahzurah (رضى الله عنه) says that the holy Prophet Muhammad (صلى الله عليه وسلم) taught me 19 words of azan and 17 words of iqamah. (Tirmidhi) The words of iqamah would be 17 only when each word is read twice. However, the Three Imams hold the following hadith as their proof:
عن أنس بن مالك قال: أمر بلالا أن يشفع الأذان ويوتر الإقامة .
Hadhrat Anas (رضى الله عنه) says that Hadhrat Bilal (رضى الله عنه) was asked to say the word of azan twice and iqamah in odd numbers. (Tirmidhi)
According to Ahnaf, Itar (odd numbers) means itar sauti i.e. 2-2 words should be said in single break, which is supported by the two above mentioned hadith. Also takbir is 2-2 times in the beginning and ending as per the Three Imams which.according to them is said two times but in single break, so they also call it single when it is called in one break. Thus it is not a far interpretation to mean itar sauti from itar in the hadith of Hadhrat Anas (رضى الله عنه). Other people too do the same interpretation when needed.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband