Allah, the Exalted, says:

"The believers are nothing else than brothers (in Islamic religion).'' (49:10)

"Verily, those who like that (the crime of) illegal sexual intercourse should be propagated among those who believe, they will have a painful torment in this world and in the Hereafter.'' (24:19)

1577. Wathilah bin Al-Asqa` (May Allah be pleased with him) said: The Messenger of Allah (PBUH) said, "Do not express pleasure at the misfortune of a (Muslim) brother lest Allah should bestow mercy upon him and make you suffer from a misfortune.''
[At-Tirmidhi].

Commentary: A true believer is one who feels unhappy to see Muslims suffering, and rejoices on the happiness of his other fellows in Faith. It is contrary to the conduct of a true believer to rejoice over the trouble of another Muslim as this attitude is very much disliked by Allah. There is every possibility that Allah may punish such a person in this world and relieve the one who is in trouble. See also Hadith No. 1571.