Article 389 of Civil Code

If the original debtor transfers his debt by an unrestricted transfer, and has against the transferee debtor a debt or a deposited or usurped specific thing, he shall retain after the transfer the right to demand the debt or thing from the transferee debtor until the latter pays the transferred debt to the transferee creditor. If the transferee debtor makes payment to the transferee creditor, what he owes shall be extinguished by set-off to the extent of what he paid.