Musnad Abu Ya'la al-Mawsili 1:122

Ishaq narrated to us, Yahya ibn Abi Bukayr narrated to us, Shu'bah narrated to us, he said: Yazid ibn Khumayr informed me, he said: I heard Sulaym ibn 'Amir, a man from Himyar, narrating from Awsat ibn Isma'il ibn Awsat al-Bajali, from Abu Bakr, that he said when the Messenger of Allah (peace and blessings of Allah be upon him) passed away: The Messenger of Allah (peace and blessings of Allah be upon him) stood among us last year in this same position of mine, then he said: "Ask Allah for *al-mu'afah* (well-being/immunity from trials), for no one has been given anything better after certainty than *al-mu'afah*."