Musnad Ahmad 696:9

Affan narrated to us, from his book, Sulayman narrated to us, Thabit narrated to us, from Ibn Abi Layla, from Suhayb, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am amazed by the affair of the believer. Indeed, the entire affair of the believer is good for him; that is not for anyone except the believer. If good fortune befalls him, he is grateful, and it is good for him. And if adversity befalls him, he is patient, and it is good for him."