The Messenger of Allah ﷺ said, "How remarkable is the affair of the believer! All of his affairs are good, and this is not the case for anyone except the believer. If something pleasing befalls him, he gives thanks, and that is good for him. If something harmful befalls him, he endures it patiently, and that is good for him."
قال رسول الله ﷺ: عجبا لأمر المؤمن، إن أمره كله خير، وليس ذاك لأحد إلا للمؤمن، إن أصابته سراء شكر فكان خيرا له، وإن أصابته ضراء صبر فكان خيرا له.
Muslim narrated it in the Book of Zuhd and Raqaiq (2999) through several routes from Sulayman bin Mughira, who said, "Thabit narrated to us, from Abdul-Rahman bin Abu Layla, from Suhayb," and he related it. There are other hadiths with the same meaning mentioned in the Book of Funerals.