Musnad Ahmad 1153:785

Aswad ibn Amir narrated to us, he said: Sharik narrated to us, from Abu Ishaq, from al-Bahiy, from Aisha, or from Ibn Umar—Sharik was uncertain—that the Prophet, peace and blessings of Allah be upon him, prostrated upon the *khumrah* (a small prayer mat made of palm leaves).