Does the prayer of the congregant become invalid if the Imam begins reciting Surat Al-Fatihah before standing upright, or completes it while descending for rukoo‘ (bowing)?

The prayer of the ma'mum (follower) is not invalidated if the imam (leader) begins reciting Al-Fatiha while still rising (not yet fully erect); rather, this is merely makruh (disliked). The karaha (dislike) is stronger if the recitation occurs in a posture other than standing. Similarly, the ma'mum should not delay in following his imam, for following is obligatory.