Musnad Ahmad 1153:1817

Bahz narrated to us, Hammad narrated to us, from Ali ibn Zayd, from Umayyah, that she asked Aisha about this verse: "Whether you disclose what is in your selves or conceal it, Allah will bring you to account for it" [Al-Baqarah: 284], and about this verse: "Whoever does evil will be recompensed for it" [An-Nisa: 123]. She said: "No one has asked me about them since I asked the Messenger of Allah, peace and blessings of Allah be upon him, about them. He said: 'O Aisha, this is Allah the Almighty’s following up with the servant regarding what afflicts him of fever, misfortune, and a thorn, even the item he places in his sleeve and then loses, so he becomes alarmed by it, then finds it in his garment. So much so that the believer emerges from his sins just as red gold emerges from the furnace.'"