Musnad Ahmad 1013:74

Ishaq ibn Isa narrated to us, Abd al-Aziz ibn Abi Hazim narrated to us, from his father, from Sahl ibn Sa’d, that he was asked about the pulpit: "From what wood is it?" He said: "By Allah, I certainly know from what wood it is, and I know who made it, and on what day it was made, and on what day it was placed. I saw the Prophet, peace and blessings of Allah be upon him, on the first day he sat upon it. The Prophet, peace and blessings of Allah be upon him, sent word to a woman who had a young carpenter, and he said to her: 'Order your young carpenter to make me some pieces of wood that I may sit upon when I speak to the people.' So she ordered him, and he went to the forest and cut some tamarisk wood, and he made the pulpit with three steps. She sent it to the Prophet, peace and blessings of Allah be upon him, and it was placed in this position of yours that you see. He sat upon it the first day it was placed, and he said 'Allahu Akbar' while upon it, then he bowed, then he descended backwards, then he prostrated, and the people prostrated with him. Then he returned until he finished. When he turned away, he said: 'O people, I only did this so that you may follow me and learn my prayer.' It was said to Sahl: 'Was there anything to the matter of the trunk [of the date palm] as the people say?' He said: 'There was indeed that which there was.'"