Abu Dawud

Hadith Commentary: Benefits and Issues: If the caravan people keep a dog merely out of fondness, not for the protection of the caravan or for alertness and awareness against thieves, and likewise, if a bell is kept without necessity or purpose, merely for adornment and decoration and out of fondness, with no need or objective, then both of these things are considered disliked (makruh) according to the majority of jurists (jumhur fuqaha). If, however, they are for a genuine need, then some have allowed their permissibility, because the Prophet (sallallahu alayhi wa sallam) permitted keeping a dog for crops and livestock.

Explanation:
1:
Such dogs that are used for hunting or guarding are exempt from this ruling.
Hanging a bell around a horse’s neck informs the enemy about the presence of the horse’s owner;
therefore, it has been disliked.
And by “bell” is meant anything that, when hung around the animal’s neck, produces sound with movement.