While I was praying in the mosque, I heard music. Should I detest it in my heart?

Enjoining what is right and forbidding what is wrong should be done according to one's capacity and ability. Playing music is a reprehensible act that must be denounced. The lowest degree of denunciation is to hate the reprehensible act in one's heart. A worshipper should hate music if he hears it, while maintaining his focus and concentration on his prayer.