Musannaf Ibn Abi Shayba 3:2115

Abu Bakr narrated to us, he said: Ali bin Hashim narrated to us, from Ibn Abi Layla, from al-Sha’bi, who said: I prayed behind al-Mughira bin Shu’bah. He stood up in the second [rak'ah], so the people glorified Allah (said "SubhanAllah") to him, but he did not sit. When he finished the prayer and turned away, he performed two prostrations while he was sitting. Then he said: "This is how I saw the Messenger of Allah (ﷺ) do."