Reference: Siyar A’laam an-Nubalaa – Volume 7, Page 107
al-Waleed ibn Mazyad said:
al-Awzaa’ee was asked about the imaam who forgetfully missed a prostration, and the congregation had [then] departed [after completing the prayer].
He said: ‘Every one [of the congregation] should individually prostrate a prostration [of forgetfulness].’