What is the ruling on completing a dhikr (remembrance of God) during prayer while starting the next pillar, such as completing "Rabbi ighfir li (O my Lord, forgive me)" while descending for prostration?

Completing the remembrance (dhikr) while beginning the next posture in prayer is contrary to the Sunnah, but the prayer is not invalidated by this incorrect action, because the remembrance is prescribed in prayer, even if it is not in its proper place. Some scholars are of the opinion that the prayer is invalidated if one intentionally does that. Ibn Qudamah said that performing a prescribed remembrance in prayer in an improper place, such as reciting (Qur'an) in bowing (ruku') and prostration (sujud), does not invalidate the prayer. Al-Mardawi added that the prayer is not invalidated intentionally, and prostration of forgetfulness (sujud as-sahw) is not required for it. Whereas Ibn Muflih narrated that some scholars said that the prayer is invalidated by intentionally doing so. Ibn 'Uthaymeen favored the opinion that the prayer is not invalidated, and that the prohibition is not for the act itself, but for its location.