Probably “vacana” here does not stand for an exact quotation but for an abbreviated statement of Īśopaniṣad 1-2, which contain “kurvann eveha karmāṇi” and “tena tyaktena bhuñjīthāḥ”. Note "ca”.

On Jun 1, 2015, at 10:57 PM, Greg Bailey <Greg.Bailey@latrobe.edu.au> wrote:

The pādas: yad idaṃ vedavacanaṃ kuru karma tyajeti ca / occur with minor variations four times in the Mahābhārata.

Can anybody guide me to a Vedic text that says kuru karma tyaja or something like it? I have had a quick look at a few texts, but come up with nothing.