Why do some readers read the ayat... qul huwallahu ahadunillahussamad? He continues reading instead of pausing it(ahad)...Is there any name for this rules in tajweed? The same thing with ayat... lumazatinillalladhee...he continues reading instead of pausing..(lumaza )....
It is sunnah to stop at the end of an aayah and take a breath before reading the next aayah, but it is not forbidden to join two aayaat together. When we do that, we must pronounce the vowel on the end of the first aayah and join it with the first pronounced letter of the next sequential aayah.
In the two aayaat exampled in the question there are tanweens at the end of each of both aayaat followed by a sukoon as the first pronounced letter of the next aayah. In Arabic there is a forbiddance of two saakin letters meeting between two words, and the tanween has a noon saakinah as the last pronounced part of it.
When there are two saakin letters meeting, the first letter changes so that there will no longer be two saakin letters meeting. In the case of the tanween for the recitation of Hafs, the noon saakinah of the tanween will always acquire a kasrah. This is why you hear a kasrah on the noon saakinah of the tanween in both aayaat in the question.
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