Why is noon sakinah followed qaf and kaf is ikfa and they are mutabaaidan?
Wa alaikum assalaam wa rahmatullahi wa barakatuh,
The Qur'an was revealed in the pure Arabic language which was they way the Arabs talked for the most part at that time. The ikhfa', ith-har, idhgaam that we know now, was all part of their natural speech, with some variations from area to area and dialect to dialect.
Later as more non-Arabs entered Islam, there was a need to write out the rules of recitation, now called tajweed, so all could understand the way to properly recite the Qur'an.
The written rules we study now were not the essence of recitation, but a by-product to explain how proper recitation was done by the Prophet, peace and blessings of Allah upon him, the companions, and those who followed.
The reasons for rules are linguistic theories put forth by those who have studied tajweed, they may not always fit the way we recite. What we need to remember is the essence is the way the Prophet, peace and blessings of Allah upon him recited, not the written rules and the reasons for the rules.
The noon as-saakinah and tanween are recited with an ikhfa' when followed by a
, this is the essence and the way all of the sound chains recite these combinations. Indeed, one of the ten qira'aat also makes an ikhfa' when the noon as-saakinah or tanween is followed by a
, so we cannot make the theory be our thermometer of how to recite in all cases, instead we take from those who have an authentic chain of recitation and learn to recite from them. The theory helps us understand the reason, but is not infallible.
Wa assalaam alaikum