Sahih Muslim Book 6 – Hadith 175-176
Chapter 19: Salat al-Awwabin (the prayer of the penitent) is when the young camels feel the heat of the hot sand.
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. (Sahih Muslim Book 6 – Hadith 175)
Zaid b. Arqam reported that the Messenger of Allah (ﷺ) went out to the people of Quba’ and saw them observing prayer; upon this he said:
The prayer of the penitent should be observed when the young weaned camels feel heat of the sun. (Sahih Muslim Book 6 – Hadith 176)
Sahih Muslim Book 6 – Hadith 175-176