Musannaf Ibn Abi Shayba 3:2119

Abu Khalid al-Ahmar narrated to us, from Ibn 'Awn, from al-Sha'bi, that al-Nu'man ibn Bashir prayed, and he rose [from the first sitting] during the two rak'ahs. So they glorified Allah (said "SubhanAllah") for him, but he continued. When he finished, he performed the two prostrations of forgetfulness while he was sitting.