The ruling on intentionally adding to the prayer

Question:
So if one intentionally adds something of the same kind as the prayer, such as standing, bowing, prostrating, or sitting, is the prayer invalid?

Answer:
Yes, if one intentionally adds standing, bowing, or prostrating to the prayer, his prayer is invalid because he intentionally contradicted what is prescribed in the prayer, so his prayer is invalid. For example, if he says, "The Fajr prayer is two rak'ahs, but I will add one or two rak'ahs," this is considered doing good, but we say your prayer is invalid because you intentionally contradicted what Allah (Glorified and Exalted is He) prescribed, so your prayer is invalid. The same applies to the other obligatory prayers; nothing is added to them or subtracted from them, but they are performed exactly as established from the Messenger (peace and blessings be upon him). Yes.