Musnad Ahmad 402:2

Abdullah ibn Ahmad said: Uqbah ibn Mukram al-Ammi narrated to us, he said: Salm ibn Qutaybah narrated to us, from Yunus ibn Abi Ishaq, from Isma'il ibn Awsat, from Khalid ibn Abdullah, from his grandfather Asad ibn Kurz, that he heard the Prophet, peace and blessings of Allah be upon him, saying: "The sins of the sick person fall away just as the leaves of a tree fall away."