Musnad Abu Ya'la al-Mawsili 209:140

Abu Khaythama narrated to us, Affan narrated to us, Wuhayb narrated to us, Khalid narrated to us, from Abu Qilabah, from some of the children of Umm Salamah, from Umm Salamah: That the Messenger of Allah (may Allah bless him and grant him peace) used to pray upon the khumrah (a small prayer mat made of palm leaves).