Is prostration for forgetfulness (Sujud as-Sahw) obligatory in voluntary prayers (Nawafil)?

Primary text

Prostration for forgetfulness carries the same ruling as in obligatory prayers (Fard), according to the general consensus of scholars. This is supported by the general statement of the Prophet, peace be upon him, "If one of you forgets, let him prostrate two prostrations," and another saying, "If one of you forgets and adds or subtracts, let him prostrate two prostrations," with no distinction made. Furthermore, since voluntary prayer involves bowing and prostration, prostration for its forgetfulness is required, similar to the obligatory prayer.