The extent of the shadow when the Messenger of Allah prayed (the noon prayer) was three to five feet in summer and five to seven feet in winter.
Sunan Abi Dawud Book 2, Hadith 10
← Previous Hadith I would offer my noon prayer with the Messenger of Allah (ﷺ) and took a handful of gravels so that they might become cold in my hand and I placed them (before me) so that I may put my forehead on them at the time when I would prostrate. I did this due to the intensity of heat.

Sunan Abi Dawud Book 2, Hadith 9 Next Hadith → We were in the company of the Prophet (ﷺ). The mu'adhdhin intended to call for the Zuhr prayer. He said: Make it cooler. He then intended to call for prayer. He said twice or thrice: Make it cooler. We then witnessed the shadow of the mounds. He then said: The intensity of heat comes from the bubbling over of the Hell ; so when the heat is violent, offer (the Zuhr) prayer when it becomes cooler.

Sunan Abi Dawud Book 2, Hadith 11