Praise be to Allaah.
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.”
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).