Reference for Ketubot 186:9

אמר רב נחמן אמר רבה בר אבוה לא הותירו זוזי חדתי פחתו אסתירא דצוניתא:

Nahman replied in the name of Rabbah b. Abbuhah: No; they made “a profit” [by receiving] new coins and “they made a loss” [by the deterioration of a coin into] an istira that was only suitable for covering a wound.

Jastrow