It is narrated from Ibn Buhaina (may Allah be pleased with him) that the Messenger of Allah (ﷺ) led us in (a four-unit prayer) and prayed two units, then stood up without sitting for the first tashahhud, and the people also stood up with him. When the prayer was completed, we began to wait for him to say the salam. He said "Allahu Akbar" and, before the salam, performed two prostrations while sitting.
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 329
Hadith Takhrijأخرجه البخاري: السهو، باب يكبر في سجدتي السهو: 1230.