don’t rejoice in sin
Quran: "Those who stayed behind were glad to remain behind and not go with the Messenger." (At-Tawbah: 81)
Quran: "This is because you were happy with what was wrong on the earth, and because you were glad when you did wrong." (Ghafir:75)
Being glad about doing wrong only darkens the heart. The better happiness is when we do what Allah loves.
May Allah make our joy in what pleases Him.
(from Syajaratul Ma’arif, Syaikh al-‘Izz bin Abdus Salam)