In all cases of mutual debts and mutual credits between the parties, the account between them shall be stated, and one debt set off against the other, and the balance only shall be allowed and paid. But no set-off or counterclaim shall be allowed of a claim in its nature not provable against the estate; provided, that no set-off or counterclaim shall be allowed in favor of any debtor to the insolvent of a claim purchased by or transferred to such debtor within thirty (30) days immediately preceding the filing, or after the filing of the petition by or against the insolvent.

SOURCE: CCP § 1355.