What is the ruling on the obligatory prayer if the worshiper begins the opening takbeer while standing, and completes it while descending for rukoo‘ (bowing)? Is this a matter of scholarly disagreement, and what is the stronger and weaker opinion on it?

The issue of a latecomer (masbuq) saying the takbir for consecration (takbirat al-ihram) while descending to catch the bowing (ruku') with the Imam is a matter of scholarly disagreement. Some jurists hold that the prayer is invalid. Others believe it becomes a supererogatory (nafl) prayer, not an obligatory one (fard). Still others maintain its validity as an obligatory prayer. Al-Mardawi stated that the takbir must be said while standing in an obligatory prayer; otherwise, the prayer becomes supererogatory. Sheikh Ibn Uthaymeen chose the view that it does not count as an obligatory prayer but as a supererogatory one. Al-Nawawi held that the takbirat al-ihram must be uttered with all its letters while standing; otherwise, the prayer does not count as an obligatory prayer. As for the Malikis, they believe that the prayer is valid for the latecomer in this situation. Nevertheless, the opinion of invalidity is more cautious, and the worshiper should utter the takbirat al-ihram completely while standing.