Majma al-Zawaid — Hadith 3814

Sayyiduna Utbah bin Mas'ud (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "How amazing is the believer and his distress over illness! If he knew what reward he receives for illness, he would love to remain ill forever." The narrator says: Then the Prophet (peace and blessings be upon him) raised his blessed head towards the sky and laughed. It was said: "O Messenger of Allah! Why did you raise your head to the sky and laugh?" The Prophet (peace and blessings be upon him) said: "I was amazed at two angels. They were looking for a servant at the place of prayer where he used to be, and the two angels did not find him. So they both went back and said: 'O our Lord! We used to record for Your such-and-such servant, every day and night, the deeds he used to do. Now we have found that You have confined him in Your rope (that is, made him ill).' Allah Almighty said: 'Record for My servant the same deeds he used to do every day and night, and do not reduce anything from them. As long as I have confined him, his reward is upon Me, and he will have the reward of the deeds he used to do before.'"
Al-Tabarani recorded it in al-Mu'jam al-Awsat, and al-Bazzar recorded it in abridged form. Its chain contains a narrator, Muhammad bin Abi Humayd, and he is extremely da'if (weak).