Musnad Abu Ya'la al-Mawsili 217:1

Zakariya ibn Yahya al-Wasiti narrated to us, Hushaym narrated to us, from al-Shaybani, from Abdullah ibn Shaddad, from his maternal aunt Maymunah bint al-Harith, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to pray on the khumrah (a small prayer mat made of palm leaves).