Sahih al-Bukhari 629
صحيح البخاري#629SahihNarrated Abu Dhar: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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 10:26