Sahih Al Bukhari (500)

عن أبي ذر قال [كنا مع النبي صلى الله عليه وسلم في سفر فأراد المؤذن أن يؤذن فقال له أبرد ثم أراد أن يؤذن فقال له أبرد ثم أراد أن يؤذن فقال له أبرد حتى ساوى الظل التلول فقال النبي صلى الله عليه وسلم إن شدة الحر من فيح جهنم]

Abu Dhar (may Allah be pleased with him) narrated: We were in the company of the Prophet (peace be upon him) on a journey and the Mu’adh-dhin wanted to pronounce the Adhan for the (Zuhr) prayer. The Prophet (peace be upon him) said to him, “Let it become cooler.” Then he again wanted to pronounce the Adhan but the Prophet (peace be upon him) said to him, “Let it become cooler.” The Mu'adh-dhin again wanted to pronounce the Adhan for the prayer but the Prophet (peace be upon him) said, “Let it become cooler,” till the shadows of the hillocks become equal to their sizes. The Prophet (peace be upon him) added, “The severity of the heat is from the raging of Hell.”