The above issue, where the Borrower actually said "Collection will be from this object from now" when presenting the Collateral/Liened Property: Pesachim 31b
Collection from non-liquid Property
Collecting the fruits of a field, to repay an outstanding debt of the field's seller: Bava Metzia 14b, 15a
Collecting from Sales or Sanctification of the Debtor, if done during the time of debt: Pesachim 30b-31b
Payback doesn't require Witnesses, even if the loan was extended before witnesses: Ketuvot 18a
Rabbinic institution protecting Purchasers, forbidding Collection from Third-Party property where the Borrower still has property: Bava Kama 8b
Collecting from a Purchaser who declares preference for not following the Above-Mentioned Institution, because he will benefit more this way: Bava Kama 8b
Institution of returning land used to pay off a debt, if the borrower comes up with cash: Bava Metzia 35b