It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) that he said: I used to pray Zuhr with the Messenger of Allah (peace and blessings be upon him). I would take a handful of pebbles in my hand so that they would cool down, and I would place them at the spot of my prostration so that I could prostrate on them (avoiding the heat of the ground); (this was because of the intensity of the heat).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2067