Does the rule of Tajweed apply to the recitation of Athaan and Iqaamah for Salaat? What are the proofs?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

According to the reciters of the Quran there are several principles in Tajweed (articulating every letter from its articulation point and giving the letter its rights and due characteristics) which must be observed according to the Arabic language with regard to properly pronouncing the words and articulating every letter from its proper place while avoiding any improper pronunciation which are referred to as obvious mistakes according to the scholars of Quran recitation, and these have to be observed when calling Athaan and Iqaamah.

[The rights of the letters are its required characteristics that never leave it.  The dues of the letters are its presented characteristics that are present in it some of the time, and not present at other times, i.e. the Madd (extending ones voice whilst pronouncing a letter), Idghaam (joining two letters together to form one letter)].

When not observing these articulation rules, one drifts away from the Arabic language and causes deficiency in the pronunciation, especially that the Muslim jurists conditioned the validity of Athaan to be in accordance to the rules of the Arabic language. However, the principles of Tajweed that are not required in the Arabic language, like Ghunnah (which is a sound that comes out from the nasopharynx)  and Idghaam; not observing such rules is considered as hidden mistakes and thus, do not have to be observed when calling the Athaan, and it is only desirable.

Indeed the jurists are of the view that calling the Athaan in a good voice is desirable because it attracts people to it and makes them love it. When calling the Athaan, one must give heed not to call it with hastiness and must properly extend his voice where it applies, contrary to calling Iqaamah where such rules may be overlooked.

Allaah Knows best.