Sahih Bukhari | Volume 1 | Hadith Number 602

Narrated by Abu Dhar
We were in the company of the Prophet on a journey and the Mu'adhdhin wanted to pronounce the Adhan for the (Zuhr) prayer. The Prophet 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 said, "Let it become cooler," till the shadows of the hillocks become equal to their sizes. The Prophet added, "The severity of the heat is from the raging of Hell."