What is the ruling on the madd (lengthening) in the Qur'an and the word "ad-dallin" (those astray) in prayer?

"Tajwid madd (lengthening) is of two types: original (natural) which does not require a reason and its duration is two counts, and secondary which requires a reason such as a hamza or sukoon. Secondary madd is divided into necessary, obligatory, and permissible. The madd in the word "al-āna" is a necessary madd, as it is followed by a light sukoon. Shortening this madd does not invalidate the prayer because it is a melodic error (lahn) that does not corrupt the meaning."