Modulation and elongation of vowels in the Adhan
Question

What is the ruling on Singing the Adhan and elongating the vowels. The hadith that speaks against singing implies getting paid also. Is singing the adhan by itself forbidden or not?
Praise be to Allah.It is not permissible to sing the adhan, but this is not like the prohibition of singing itself; it varies between being makrooh or being haram, unless the meaning is altered, in which case it becomes haram.
Zayn al-Deen al-‘Iraaqi said:
It is mustahabb to elongate the vowels slightly in the adhan, but it is makrooh to elongate them too much in the manner of singing, because it was narrated that a man said to Ibn ‘Umar, “I love you for the sake of Allah,” and he replied, “I hate you for the sake of Allah, for you overstep the mark in your adhan.” Hammaad said, he meant singing.
Wali al-Deen al-‘Iraaqi said:
Al-Shaashi said in al-Mu’tamad: the correct way is for the voice to have a soft and sad tone, not harsh like the speech of the Bedouins or soft like the voice of one who is dying… The author of al-Haawi said: Overstepping the mark means speaking in an emphatic and exaggerated manner. He said, it is makrooh to make the adhan like singing because it makes it incomprehensible, and because the salaf did not do that, rather it is something that was innovated after their time.
(Tarh al-Tathreeb, 3/118-120)
Ibn al-Haaj said:
Chapter on the prohibition of making the adhan like singing
One must be careful to avoid giving a tune like singing to the adhan, and one must also tell others not to do things that they have innovated by making it resemble singing, whereby it is given a joyful tune like singing until one cannot tell what they are saying in the words of the adhan, and it is just voices going up and down. This is a repulsive recently-invented bid’ah (innovation) which some governors introduced in a school that they had built, then it spread from there. This adhan is done in Syria at this time, and it is a vile innovation, because the purpose of the adhan is to call people to prayer, so the words must be made understandable to the listener – but in this adhan nothing can be understood, because the words have been changed into something that resembles singing. It was narrated in the hadeeth that the Prophet (peace and blessings of Allah be upon him) said: “Whoever innovates something in this matter of ours (i.e., Islam) that is not part of it, will have it rejected.” Imaam Abu Taalib al-Makki (may Allah have mercy on him) said in his book: one of the things that they have innovated is modulation (varying the tone) in the adhan, which is a kind of exaggeration and overstepping the mark. One of the muezzins said to Ibn ‘Umar, “I love you for the sake of Allah,” and he replied, “But I hate you for the sake of Allah.” He asked, “Why, O Abu ‘Abd al-Rahmaan?” He said, “Because you exaggerate in your adhan, and you accept payment for it.” Abu Bakr al-Aajurri (may Allah have mercy on him) used to say, I left Baghdaad and I cannot stay there because of the innovations that they have introduced into everything, even in Qur’aan recitation and the adhan – meaning that they accepted payment for it and they had introduced modulation (varying the tone or pitch, like singing). (al-Madhkal 2/245, 246)
4. It was said in al-Mudawwanah: it is makrooh to sing in an emotional tone in the adhan. And it was said in al-Tiraaz that singing in an emotional tone means making the voice go up and down, which stems from the loss of equilibrium which happens when a person experiences extremes of happiness or grief; it is a kind of confusion or panic.
It was said in al-‘Atbiyah that giving an emotional tone to the adhan is munkar (to be denounced). Ibn Habeeb said: (it is also makrooh) to give it a grieving tone without singing. The letters should not be altered or sung. The Sunnah is to enunciate it clearly in a loud voice.
Ibn Farhoon said: singing in en emotional tone means making short vowels long and long vowels short. ‘Abd-Allah ibn ‘Umar heard a man doing this in his adhan, and he said, “If ‘Umar were alive, he would break your jaw!” Ibn Maaji said, Singing the adhan in an emotional tone is makrooh, because it goes against humility and dignity, and takes the pattern of singing. The degree to which it is makrooh depends on the type, if it does not reach the level of promiscuous singing; if it does reach that level, then it is haram. Ibn Habeeb made a connection between a sad tone and a joyful tone, as narrated by Abu Muhammad.
From this it may be understood that it is mustahabb for the muezzin to have a pleasant and loud voice, and for his voice to resonate. It is makrooh for him to have a harsh and unpleasant voice, and to give the adhan a joyful or a sad tone; if that reaches extreme levels, then it is haram.
(Mawaahib al-Jaleel by Hattaab, 1/437, 438)
Shaykh Muhammad ibn Ibraaheem (may Allah have mercy on him) said:
One should not elongate excessively in the adhan, and if doing so distorts the meaning, then it invalidates the adhan. If the elongated letters (huroof al-madd) are made longer than necessary, this should not be done, and if regular vowels are elongated in a manner that changes the meaning, this invalidates the adhan, otherwise it is makrooh.
(Fataawa al-Shaykh Muhammad ibn Ibraaheem, 2/125)
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
The mulahhan or the one who introduces modulation into the adhan is the one who gives the adhan in the manner of singing, as if he is singing the words of a song. His adhan is valid but it is makrooh.
The malhoon is the one who makes grammatical mistakes, i.e., he goes against the rules of the Arabic language. But this falls into two categories, those which invalidate the adhan, which are those which alter the meaning, and those with which the adhan is still valid, but it is makrooh, which do not alter the meaning. So if the muezzin says “Allahu akbaar”, the adhan is not valid, because he is changing the meaning. Akbaar is the plural of kabar, just as asbaab is the plural of sabab. Kabar is a kind of drum  (Al-Sharh al-Mumti’, 2/62, 63)
And Allah knows best.