Sayyiduna Khawwat bin Jubayr (may Allah be pleased with him) narrates: I fell ill, and the Prophet (peace and blessings be upon him) came to visit me. When I recovered, the Prophet (peace and blessings be upon him) said: "Your body has become healthy, so fulfil the promise you made to Allah Almighty." I said: "I did not make any promise to Allah Almighty." The Prophet (peace and blessings be upon him) said: "Every patient who falls ill makes some vow or intends some good deed, so fulfil for Allah Almighty the promise you made to Him."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains Abdullah bin Ishaq al-Hashimi, whom al-Uqayli declared da'if (weak).