Musannaf Ibn Abi Shayba 3:2144

Ibn ‘Ulayyah narrated to us, from Yunus, who said: An Imam of the congregational mosque became confused, but he did not perform the two prostrations of forgetfulness. Some of the people performed them, and some did not. This was mentioned to al-Hasan, and he did not see any obligation of prostration upon them. It was mentioned to Ibn Sirin, and he preferred the action of those who had performed the prostrations.