I used to pray Zuhr with the Messenger of Allah ﷺ, and I would take a handful of pebbles to let them cool in my palm, then place them where I would put my forehead in prostration, because of the intense heat.
كنت أصلي الظهر مع رسول الله ﷺ فآخذ قبضة من الحصى لتبرد في كفي أضعها لجبتهي أسجد عليها لشدة الحر.
It was narrated by Abu Dawud (399) and Nasai (1081), both from the hadith of Abbad bin Abbad, who said, our teacher Muhammad bin Amr narrated to us, from Saeed bin Harith Ansari, from Jabir bin Abdullah, and he mentioned something similar. Its chain of transmission is hasan because of Muhammad bin Amr Laythi, and Ibn Hibban graded it sahih (2276), narrating it through Abdul-Wahhab Thaqafi, who said, Muhammad bin Amr narrated it to us with this wording, "We used to pray with the Prophet ﷺ during intense heat, so one of us would take a handful of pebbles and put them in this hand of his, then in this hand of his, and when they had cooled he would prostrate on them."As for what was narrated from Jabir, who said, I asked the Prophet ﷺ about smoothing the pebbles during prayer, and he said, "Once, and if you refrain from it, that is better for you than a hundred camels, all of them black-eyed," this is daif. It was narrated by Ahmad (14204), Ibn Khuzayma (897), and Abd bin Humayd (1145), all of them through routes from Ibn Dhi'b, from Shurahbil bin Saad, from Jabir, and he mentioned it. Shurahbil bin Saad was declared daif by Nasai and others, and his memory became confused toward the end of his life, so his narration necessarily requires corroboration.