Jami` at-Tirmidhi 193
جامع الترمذي#193SahihAnas bin Malik narrated:"Bilal was ordered to make the phrases of the Adhan even, and the phrases of the Iqamah odd
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 2:45