Kitāb al-Muʾmin
Hadith 4949 - وعن أبي عبد الله (ع) قال: ضحك رسول الله (ص) حتى بدت نواجذه، ثم قال: ألا تسألوني عما ضحكت؟ قالوا: بلى يا رسول الله، قال عجِبتُ للمرءِ المسلم أنه ليس من قضاءٍ يقضيه اللهُ له إلاّ كان خيراً له في عاقبةِ أمره.
49. It has been narrated that Abu 'Abd Allah (a.s) said: ' The Messenger of Allah (a.s) laughed once until his teeth were showing, 'Will you not ask me why I am laughing?' he asked. 'Indeed, O Messenger of Allah,' inquired the people. 'I am amazed at a Muslim, whatever Allah decrees for him will always turn out good for him in the end,' he said.