The Messenger of Allah ﷺ used to pray on a straw mat and on tanned hide.
حدثنا عبيد الله بن عمر بن ميسرة وعثمان بن أبي شيبة بمعنى الإسناد والحديث قالا حدثنا أبو أحمد الزبيري عن يونس بن الحارث عن أبي عون عن أبيه
كان رسول الله ﷺ يصلي على الحصير والفروة المدبوغة
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[Its chain is daif] Ahmad narrated it (4/254, no. 18414) from the hadith of Yunus bin Harith Taifi, with this wording, and it is daif, the majority of scholars declared it daif. Yet Hakim graded it sahih according to the criterion of the two Shaykhs (1/259), and Dhahabi agreed with him, according to the criterion of Muslim (!). Ibn Hibban pointed out a break in the chain between Mughira and the one who narrated from him.As for praying on a mat, that is established, see no. 612 and the previous hadith.