Musnad Abu Ya'la al-Mawsili 219:10

Abu Khaythama narrated to us, Wahb ibn Jarir narrated to us, Shu'bah narrated to us, from Abu Hasin, from Yahya ibn Waththab, from Abu 'Abd al-Rahman, from Umm Habibah, the wife of the Prophet, may Allah bless him and grant him peace: That the Prophet, may Allah bless him and grant him peace, used to pray upon the khumrah (a small prayer mat made of palm leaves).