Musannaf Ibn Abi Shaybah 4590 — An imam who errs and does not

Yunus said: Once an imam of the Jami' mosque made a lapse in the prayer and did not perform the prostrations of forgetfulness. Some of the people performed the prostration of forgetfulness and some did not. The matter was put to al-Hasan, and he said that in this case prostration is not obligatory on the people. It was mentioned to Ibn Sirin, and he preferred the action of those who had prostrated.