The  (changing) of the  saakinah and tanween is defined in applied tajweed as: The changing of noon saakinah or  the tanween into a , when followed by a  with the observance of a lengthened ghunnah on the letter . 

If the letter occurs immediately after a  saakinah in the same word, or between two words (meaning the  saakinah or the tanween would be at the end of word, and the the first letter of the next word), it is then required that the reader changes the  saakinah or tanween into a hidden , with a ghunnah present.  The  saakinah is changed into a meem in pronunciation, not in the written word.  You may note that most copies of the Qur’an have a very small meem written over or under the noon in this case, or the second line of a fat-h or kasrah tanween or dhammah of the tanween is replaced by a small meem.  The little in this case has a tail on the end of it. 

The  hidden, not by leaving a small space between the lips, as some modern scholars have said, but by closing the lips and holding the  for the length of the ghunnah, then opening them with the .  This is the correct way of “hiding” the  as written in the books of the old scholars, and as passed down in applied recitation by chains of transmission that go back to the Prophet Mohammed, . 

Examples of the :

In this first example above, the  saakinah is the last letter of the next to the last word of the written part of the aayah.  The next word, starts with the letter .  The  is then changed in pronunciation to a , and this  is held with a ghunnah, then the lips are separated pronouncing the letter . 

Click here to listen to this aayah

In this example above, the  saakinah is in the middle of the word and followed by the letter .  The  saakinah is changed into a  just as in the previous example.

These two different aayaat are examples of the tanween being followed by the letter .  The , or changing of the  saakinah of the tanween into a , is done in the same way as the other examples.  The little  can be seen written over all of these examples.  The little  takes the place of the second dhammah, fat-h, or kasrah of the tanween.