How did the scholars know that young camels stand up due to intense heat before noon, and what is their evidence for that, given their statement that the Duha prayer should not be performed before noon, based on the Prophet's saying that the Duha prayer is when the young camels feel the heat of the sand?

The Dhuha prayer begins after the sun has risen and ascended by the measure of a spear, and extends until just before noon. Its best time is when the heat intensifies, at the passage of one-quarter of the day, which is known as "when the young camels' hooves burn," meaning when the soles of young camels' feet burn from the intense heat of the sand, forcing them to seek shade. This does not require proof because it is a observable phenomenon.