Bukhari

Hadith Commentary:
Prophet Dawud (alayhis salam) was granted the miracle of a melodious voice. Whenever he would recite the Zabur with his beautiful voice, a wondrous atmosphere would be created. The Messenger of Allah (sallallahu alayhi wa sallam) has alluded to this very matter.

Hadith Commentary:
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"Mazamir" is the plural of "mizmar," which is a musical instrument.
Here, it refers to melodiousness.
Allah granted Prophet Dawud (alayhis salam) the miracle of a beautiful voice; when he would recite the Zabur, an extraordinary atmosphere would be created.
Even the mountains and birds would produce similar sounds, as is explicitly mentioned in the Noble Qur’an.
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Abu Musa al-Ash‘ari (radi Allahu anhu) was also very melodious.
The Messenger of Allah (sallallahu alayhi wa sallam) would listen to his recitation with great attentiveness.
The Messenger of Allah (sallallahu alayhi wa sallam) likened Abu Musa’s (radi Allahu anhu) melodiousness to the melodiousness of Dawud (alayhis salam).
(Sunan al-Nasa’i, al-Iftitah, Hadith: 1021;
and Fath al-Bari: 9/116)

Explanation:
1:
Once, the Prophet (sallallahu alayhi wa sallam) and Aisha (radi Allahu anha) passed by the house of Abu Musa al-Ash'ari (radi Allahu anhu). Abu Musa was reciting the Qur'an in a very melodious voice. The next morning, regarding this incident, the Prophet (sallallahu alayhi wa sallam) said about him:

"Mizmar" (flute) is indeed an instrument through which a beautiful sound is produced, but here only a beautiful voice is intended.

Dawud (alayhis salam) used to recite his book, the Zabur, with such melodiousness that birds flying in the sky would stop and listen to his recitation.