Musnad Ahmad 1156:106

'Affan narrated to us, Wuhaib narrated to us, he said: Khalid narrated to us, from Abu Qilabah, from one of the children of Umm Salamah, from Umm Salamah: "That the Messenger of Allah (peace and blessings of Allah be upon him) used to pray on the khumrah (a small prayer mat made of palm leaves)."