Long time, eh? May Allah forgive me for my shortcomings. :(
Volume 4, Book 52, Number 249 :
Narrated by Abu Bashir Al-Ansari (radiallaahu `anhu)
That he was in the company of Allah’s Apostle (sallallaahu `alayhi wasallam) on some of his journeys. (The sub-narrator ‘Abdullah adds, “I think that Abu Bashir (radiallaahu `anhu) also said, ‘And the people were at their sleeping places.”) Allah’s Apostle (sallallaahu `alayhi wasallam) sent a messenger ordering: “There shall not remain any necklace of string or any other kind of necklace round the necks of camels except it is cut off.”
One of the opinions on theses ‘necklaces’ is that they refer to the bells that are hung round the necks of animals. Muslim narrated in his Saheeh (2113) from Abu Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The angels do not accompany any group with whom there is a dog or a bell.”
And he narrated (2114) also from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Bells are the musical instruments of the Shaytaan.”
Al-Nawawi (may Allaah have mercy on him) said: As for bells, it was said that the reason why the angels dislike them is that they are similar to church bells, or because they are one of the hanging things that are forbidden. And it was said that the reason why they are disliked is their sound, which is supported by the report which mentions “the musical instruments of the shaytaan.”
Al-Nawawi commented on this hadith in Riyad-us-Saaliheen (chapter 307):
“Dog” here stands for that dog which is prohibited to keep. Dogs kept for the purpose of hunting and security do not fall in this category. Angels signify angels of mercy; otherwise we are attended all the time by the angels who record our deeds for us. Bell in this context refers to the bell which is placed in the neck of animals and rings when they move. End quote.
The reason why their sound is disliked is that it is akin to musical instruments, which are forbidden.
Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said: To sum up, the sound has two qualities, one which is the strength of the sound and the other is its tune, and because of its musical tune it was prohibited, and the reason was given as being because they are “the musical instruments of the shaytaan.”
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: (The Prophet (peace and blessings of Allaah be upon him)) told us that the angels do not accompany people with whom there is a bell, because when the animals walk, it will make a sound like music, and it is known that musical instruments are haraam. End quote. Sharh Riyaadh al-Saaliheen (4/340).
For further reading (in Arabic), click here.