"Bilal was ordered to make the phrases of the Adhan even, and the phrases of the Iqamah odd."
Jami` at-Tirmidhi Book 2, Hadith 45
← Previous Hadith the Prophet taught him the Adhan with nineteen phrases, and the Iqamah with seventeen phrases.

Jami` at-Tirmidhi Book 2, Hadith 44 Next Hadith → "Allah's Messenger would say each phrase of the call (for prayer) two times, for the Adhan and the Iqamah."

Jami` at-Tirmidhi Book 2, Hadith 46