‘Abdallah b. Mas'ud said, “When the Prophet sat down on the pulpit we faced him.”
Tirmidhi transmitted it, and said this was a tradition he knew only among the traditions of Muhammad b. al-Fadl who was weak and whose traditions were not accepted.
Ibn ‘Umar said that the Prophet used to deliver two sermons. He would sit down when he ascended the pulpit till he (I think he meant the mu’adhdhin) was finished. He would then stand up and preach, then sit down and say nothing, then stand up and preach.
Jabir b. Samura said, “The Prophet used to preach standing, then he would sit down, then stand and preach standing. If anyone tells you he preached sitting he is lying. I swear by God that I prayed along with him on more than two thousand occasions.”
