What is the ruling on lengthening (madd) by three or four counts in (al-ḍāllīn) during prayer?

The madd in (ad-dāllīn) is a necessary, heavy word madd (madd kalimi lāzim muthaqqal), and it is extended for six counts (ḥarakāt). Shortening the necessary madd after the alif in "walā ad-dāllīn" from Surat al-Fatiha is considered a minor error (laḥn) that does not change the meaning, and therefore does not necessitate repeating al-Fatiha or the prayer.