What is the ruling on a follower (Ma'moom) raising from bowing before his Imam does so intentionally?
Chapter on the Description of Prayer
Al-Mughni
Book of Prayer
Primary text
If the follower performs the action intentionally, there are two views regarding whether his prayer is invalidated. This is because he preceded the Imam by one essential pillar (rukn), which is analogous to preceding him in bowing entirely. If the follower performs the action out of forgetfulness (sahwan), his prayer remains valid. There are two narrations regarding whether that specific rak'ah is counted.
Supporting text
If the follower precedes the Imam by two pillars (e.g., bows and rises before the Imam bows) and then intentionally prostrates while the Imam is still rising, the prayer is invalidated because the follower did not follow the Imam for the majority of the rak'ah. If this precedence occurs due to forgetfulness, the prayer is not invalidated, and that rak'ah is not counted due to the lack of following the Imam during it.