Musnad Ahmad 1013:57

Hammad ibn Khalid narrated to us, Abdullah—meaning Ibn Umar—narrated to us, from al-Abbas ibn Sahl al-Sa’idi, from his father, that the Messenger of Allah (ﷺ) used to lean against a trunk. He said: "The people have become numerous, and if I had something," meaning: to sit upon. Al-Abbas said: So my father went and cut the pieces of wood for the pulpit from al-Ghaba. He said: I do not know whether my father made it himself or had it made.