Concerning the pronunciation of the letter Daad, as we pronounce it as a "d or th" why is it when reciting it becomes a "l" as in the last line of the surah fathihah

Question
Assalamu Alaikum,
I have a question concerning the pronunciation of the letter Daad

As we pronounce it as a "d or th" why is it when reciting it becomes a "l" as in the last line of the surah fathihah

But there has to be a correct way of pronouncing this letter.  Is it closer to a "D"  or a "TH" or "L" while reciting?

Answer
The letter  is unique to the Arabic language, it is sometimes called the language of  the .  We therefore caution against comparing it to an English letter, as it has a unique articulation point and sound, not found in any of the letters in the English alphabet.   If one compares it to an English letter, it invariably will be pronounced incorrectly. 

The is pronounced from one or both sides of the tongue and the sides collide with the molars to produce the sound of this unique letter.  The tip of the tongue is not used when correctly pronouncing , so it should not sound like the "d" or the "th" and not at all like the "l".  In the word , the has a shaddah, so is emphasized, followed by a long six vowel count alif, then there is a  with a shaddah.  So, one does here a in this word, but after the long alif.  You can listen to this word pronounced correctly here: http://abouttajweed.com/al-faa%7E4_128.mp3

Please see the following link: http://www.abouttajweed.com/articulation-points-areas-of-the-arabic-letters/the-side-of-the-t.html, and take notice of the section on common mistakes in this letter.