Musnad Ahmad 1153:371

Abu Mu’awiyah ‘Abdullah ibn Mu’awiyah al-Zubayri narrated to us—he came to us in Makkah—Hisham ibn ‘Urwah narrated to us, he said: ‘Urwah used to say to ‘Aishah: "O my mother, I do not marvel at your understanding; I say: the wife of the Messenger of Allah, may Allah bless him and grant him peace, and the daughter of Abu Bakr. And I do not marvel at your knowledge of poetry and the days of the people; I say: the daughter of Abu Bakr, and he was the most knowledgeable of people, or among the most knowledgeable of people. But I marvel at your knowledge of medicine; how is it? And from where is it?" He said: She struck his shoulder and said: "O ‘Urayyah, the Messenger of Allah, may Allah bless him and grant him peace, used to fall ill at the end of his life, or in the latter part of his life. Delegations of the Arabs would come to him from every direction, and they would describe remedies to him, and I would prepare them for him; so that is from where [it comes]."