What is the ruling on elongating the letter "أ" (alif) in the word "Akbar" during the Imam's takbir in obligatory prayer, and does it invalidate the prayer or is it reprehensible, and does it necessitate prostration of forgetfulness (sujud al-sahw)?

The madd (lengthening) in the word of Majesty "Allah" occurs on the alif between the lam and the ha. This lengthening is recommended in the takbirat al-intiqal (transitionary takbirs) but not in the takbirat al-ihram (opening takbir). The maximum madd is seven alifs (14 vocalic movements). As for adding an alif after the ba in "Akbar", this invalidates the prayer because it changes the meaning. Similarly, lengthening the hamza of "Allah", or adding an alif after the ba or geminating it, or adding a waw before the word of Majesty, or changing the hamza of "Akbar" to a waw, all invalidate the prayer.