Salat al-Awwabin (the prayer of the penitent) is when the young camels feel the heat of the hot sand Sahih Muslim 748 a
Translation
Zaid b. Arqam, on seeing some people praying in the forenoon, said
They well know that prayer at another time than this is more excellent, for Allah's Messenger (ﷺ) said: The prayer of those who are penitent is observed when your weaned camels feel the heat of the sun.