Musannaf Ibn Abi Shayba 21:62

Yahya ibn Abi Kathir narrated to us, he said: Zuhayr ibn Muhammad narrated to me, from Abdullah ibn Muhammad ibn Aqil, from Mu’adh ibn Rifa’ah ibn Rafi’ al-Ansari, from his father, he said: I heard Abu Bakr saying: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying during this summer heat of the previous year: "Ask Allah for well-being (al-‘afiyah) and certainty (al-yaqin) in the Hereafter and the first life."