It is narrated from Sayyiduna Suhayb (may Allah be pleased with him) that he said: I prayed one of the two evening prayers with the Messenger of Allah (peace and blessings be upon him). When he (peace and blessings be upon him) finished, he (peace and blessings be upon him) turned his face towards us smiling and said: "Will you not ask me why I laughed?" The Companions said: Allah and His Messenger know best. He (peace and blessings be upon him) said: "I marvel at Allah's decree for the Muslim servant: whatever Allah decrees for him is good, and there is no one for whom every decree of Allah is good except the Muslim servant."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7286