Musannaf Ibn Abi Shayba 3:1979

Hushaym narrated to us, he said: Al-Awwam informed us, from Sa’id ibn Jubayr, that the Messenger of Allah (may Allah bless him and grant him peace) recited the prostration of Surah Sad while on the pulpit. When he reached the prostration, he recited it, then he descended and prostrated.