Wathilah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Do not express joy at your (Muslim) brother's affliction, for it is possible that Allah may have mercy on him and test you with that (affliction)." Tirmidhi, and he said: This hadith is Hasan Gharib. Its chain is weak. Narrated by al-Tirmidhi.