Mudgalapurana 8.8.22

8.8.22

ato vedavādā viśeṣeṇa dhūmrā bhavanti hyaho varṇituṃ te svarūpam |
budhaiḥ kathyase dhūmravarṇastatastvaṃ namo dhūmravarṇāya sarveśvarāya ||

Therefore, the assertions of the Vedas become especially smoky (dhūmra), alas, in describing your true nature; / therefore you are spoken of by the wise as 'Dhūmravarṇa', homage to Dhūmravarṇa, the Lord of all!