Fiqh-us-Sunnah - 1.83

Hadith 1.83.1

The time for the noon prayer (dhuhr)

The previous two hadith make it clear that the noon prayer begins when the sun passes its meridian and it continues until an object's shadow is approximately the same length as the object itself. If it is extremely hot, it is preferred to delay the noon prayer until it is cooler. This is done in order to retain the humility and awe of the prayer. If this is not the case, it should be prayed early in its time. This opinion is based on the following hadith: Reported Anas, "If it was extremely cold, the Prophet, upon whom be peace, would pray early.
If it was extremely hot, he would wait for it to cool down." (Related by al-Bukhari.) Abu Dharr relates, "We were with the Prophet, upon whom be peace, on a journey.
When the caller to prayer wanted to give the adhan, the Prophet said 'Let it cool down.' This happened two or three times, until we saw the shadows of the hills. Then the Prophet said, 'The extreme heat is from the fragrance of Hell. If the heat becomes extreme, delay the prayer until it becomes cool." (Related by al-Bukhari and Muslim.) However, this delay does have a limit. According to Ibn Hajr's Fath al-Bari, "The scholars differ over how long one may wait to let the temperature cool. Some say, 'Until the shadow of an object becomes an arm's length,' or 'Until the shadow becomes one-fourth of one's height.' Others say one-third or one-half, and so on. Its ruling is according to its basic principle, and it changes with different circumstances, provided that the prayer is not delayed until the end of its time."