Does making a mistake in repeating "Allahu Akbar" or stammering an incomprehensible utterance during prayer invalidate it?

The Messenger of Allah, peace and blessings be upon him, said: "Whoever innovates in this matter of ours something that does not belong to it will have it rejected." (Agreed upon). Al-Nawawi said, "The hadith is one of the great principles of Islam and one of the most comprehensive words of the Prophet, peace and blessings be upon him. It is an explicit rejection of every innovation." And among the innovations that have appeared in our time is what you mentioned, namely sending the Qur'an via social media and requesting that it be completed within a specified period of time. This is an innovation, as it was not done by the Prophet, peace and blessings be upon him, nor by his Companions, nor by the righteous predecessors. Furthermore, it is a restriction on the unlimited grace of Allah, as Allah the Almighty said: "Recite what is easy for you of the Qur'an." (Al-Muzzammil: 20). And His saying: "And when the Qur'an is recited, listen to it and pay attention that you may receive mercy." (Al-A'raf: 204). The jurists stated that the best way to read the Qur'an is to do so with reflection and contemplation, even if it is a small amount, rather than reading a large amount without reflection and contemplation. Therefore, we advise our brothers and sisters to avoid this innovation and to adhere to the Sunnah of the Prophet, peace and blessings be upon him. Allah knows best.