It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that once the Prophet (peace and blessings of Allah be upon him) led five rak'ahs in the Zuhr prayer. The people asked, "Has there been an addition in the prayer?" So the Prophet (peace and blessings of Allah be upon him) performed two prostrations of forgetfulness (sujood as-sahw).