The Prophet ﷺ used to pray on a small prayer mat.
و قال أحمد حدثنا أبو النضر حدثنا شريك عن أبي إسحاق عن البهي
كان النبي ﷺ يصلي على الخمرة
No references are available.
Its chain of transmission is sahih. It appears in Majma al-Zawaid 2:56, where it is stated, "Ahmad, Bazzar, and Tabarani in al-Kabir and al-Awsat narrated it," and it adds, "and he prostrates upon it." The narrators of Ahmad are the narrators of the sahih. Hadith 3582 has already passed by way of Zuhayr, from Abu Ishaq, from Bahi, from Ibn Umar, "Hand me the khumrah," and so on, so perhaps this is an abridgment of that one. See also 5589.As for al-khumrah, with the kha marked with damma and the meem with sukun, Ibn Athir said, it is the size of what a man places his face upon in his prostration, made of woven reed mat or palm-leaf weaving or similar plant material, and it is not called khumrah except at this size. It was named khumrah because its threads are covered by its palm fronds. This word occurs repeatedly in the hadith, and this is how it has been explained.It is reported in Sunan Abu Dawud, on the authority of Ibn Abbas, who said, "A mouse came and began dragging the wick, and it brought it and dropped it in front of the Messenger of Allah ﷺ on the khumrah upon which he was sitting, and it burned a spot of it the size of a dirham." This is explicit in applying the term khumrah to the larger kind of it.