Is it permissible to add to the Imam's supplication (du'a) in Qunut or outside of it, such as saying "Amin, and all Muslim lands" after the Imam's supplication: "O Allah, have mercy on us and forgive us"?

Firstly: There is no harm in the congregant adding to the Imam's supplication during the Friday sermon, such as saying: "and all Muslim lands," because supplicating is permissible for the congregant during the sermon according to the Hanbalis. However, sending blessings upon the Prophet (peace be upon him) and saying "Ameen" to the Imam's supplication are sunnah, whereas making one's own supplication is merely permissible. Similarly, in a lesson of knowledge, it is permissible for the congregant to supplicate independently and in conjunction with the Imam.

Secondly: The congregant should not add to the Imam's supplication during Qunut al-Witr or Qunut an-Nawazil (calamity supplication), whether performed before or after bowing; because these are not occasions for the congregant to make their own supplication. Therefore, they should limit themselves to saying "Ameen." This is the view of the majority of jurists. If the congregant does not hear the Imam's supplication, then they should supplicate.