Musnad Abu Ya'la al-Mawsili 1:132

Ishaq ibn Isma'il narrated to us, Waki' narrated to us, from Ja'far ibn Burqan, from Thabit ibn al-Hajjaj, who said: Abu Bakr al-Siddiq stood up after the death of the Prophet, may Allah bless him and grant him peace, and said: "You know that the Messenger of Allah, may Allah bless him and grant him peace, stood among you last year and said: 'Ask Allah for well-being (al-'afiyah), for no servant has been given anything better than well-being, except for certainty (al-yaqin).' And I ask Allah for certainty and well-being."