Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
274. Chapter: On the prohibition against gloating over a Muslim's misfortune
Allah Almighty says, "The believers are brothers" (49:10)
and the Almighty says, "People who love to see filth being spread about concerning the believers, will have a painful penalty both in this life and in the Hereafter." (24:19)
1577. Wathila ibn al-Asqa' reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "Do not delight in someone else's misfortune. Allah may have mercy on him and put you to the test." [at-Tirmidhi]
There is also the hadith transmitted from Abu Hurayra about spying which was already mentioned: "Every Muslim is sacred to another Muslim."