Sahih al-Bukhari Book 10, Hadith 26
We were in the company of the Prophet (ﷺ) on a journey and the Mu'adh-dhin wanted to pronounce the
Adhan for the (Zuhr) prayer. The Prophet (ﷺ) said to him, "Let it become cooler." Then he again wanted
to pronounce the Adhan but the Prophet; said to him, "Let it become cooler." The Mu'adh-dhin again
wanted to pronounce the Adhan for the prayer but the Prophet (ﷺ) said, "Let it become cooler," till the
shadows of the hillocks become equal to their sizes. The Prophet (ﷺ) added, "The severity of the heat is
from the raging of Hell."
I came to the Prophet (ﷺ) with some men from my tribe and stayed with him for twenty nights. He was kind and merciful to us. When he realized our longing for our families, he said to us, "Go back and stay with your families and teach them the religion, and offer the prayer and one of you should pronounce the Adhan for the prayer when its time is due and the oldest one amongst you should lead the prayer."
Two men came to the Prophet (ﷺ) with the intention of a journey. The Prophet (ﷺ) said, "When (both of) you set out, pronounce Adhan and then Iqama and the oldest of you should lead the prayer."