Musannaf Ibn Abi Shayba 3:2125

Yazid ibn Harun narrated to us, from Hisham, from Muhammad, who said: Imran ibn Husayn led us in prayer in the mosque, and he stood up during the two rak'ahs, or he sat during the three—and Hisham was mostly of the opinion that he sat during the two rak'ahs. When he completed the prayer, he performed the two prostrations of forgetfulness (sajdatay al-sahw).