Al-Imaam Al-Albaani (may Allaah have mercy upon him) stated:
"The origin regarding the acts of worship is that they are not established except with the approval of the Messenger of Allaah (sallallaahu alayhi wa sallam). This is an origin that is agreed upon amongst the scholars and we do not perceive that any Muslim scholar would oppose this. If it wasn't for this foundation/principle then it would be permissible for any Muslim to add to the amount of Raka-aat of the Sunan, rather the obligatory prayers whose amount has been established by way of the action of the prophet (sallallaahu alayhi was sallam) and his consistency in performing them that way, with the claim that he (the Prophet) didn't prohibit adding to the amount! This is clear and the falsehood is apparent."
Source: Salaatu At-Taraaweeh pg. 29
Sisters Upon Al-Istiqaamah