I have been asked a question when I was defining Bida'h and the reasons why we shouldn't follow the People of innovation.
So the question was :"so does it mean that wearing the niqab is bida'h, as from what I learned niqab is not obligaroty?"
I didn't have the answer for this as I couldn't give any evidence about it, so please Insha Allah if anyone of you can help me to clarify this, may Allah reward you.
check shaykh al albani's book: The Hijaab [Jilbaab] of the Muslim Woman as in the Qur'aan and Sunnah under the heading Know that covering the face and the wrists has its basis in the Sunnah, And this was an action that was done during the time of the Prophet (sallallaahu 'alayhi wasallam)