Mishkat al-Masabih 4 Prayer كتاب الصلاة 25

وَعَنْ أَنَسٍ قَالَ: كُنَّا إِذَا صَلَّيْنَا خَلْفَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِالظَّهَائِرِ سَجَدْنَا على ثيابنا اتقاء الْحر

Anas said, “When we prayed behind the Prophet at midday in summer we prostrated ourselves on our clothing to protect ourselves from the heat.” (Bukhari and Muslim, the wording being Bukhari’s.)