Is there a sin on someone who repents from playing music if they dispose of the guitar by putting it in the trash, and then someone else uses it?

Musical instruments must be broken when one repents from using them, not merely discarded, lest someone else use them. There is no guarantee required for breaking them, and this is the view of most jurists, as mentioned by Ibn al-Qayyim in his book "Al-Turuq al-Hukmiyyah." This is further supported by the fact that Imam Ahmad issued a fatwa (definition) allowing the breaking of musical instruments. Therefore, musical instruments must be disposed of by breaking them, not merely by discarding them.