Musnad Ahmad 790:185

Khalaf ibn al-Walid narrated to us, al-Mubarak narrated to us, from al-Hasan, who said: Imran ibn Husayn informed me that the Prophet, peace and blessings of Allah be upon him, saw a ring on the upper arm of a man—I think he said it was made of brass—so he said: "Woe to you, what is this?" He said: "It is for the weakness (al-wahinah)." He said: "As for it, it will not increase you except in weakness. Cast it away from you, for if you were to die while it is upon you, you would never succeed."