Vajrasuci (Siddhacarya Ghoshapada) 11

11

mānavadharmaprāmāṇyādapi
uktaṃ hi mānave28 dharme29—
sadyaḥ patati māṃsena lākṣayā lavaṇena ca
tryahācchūdraśca bhavati brāhmaṇaḥ kṣīravikrayī

And also from the authority of the Laws of Manu.
For it is stated in the Laws of Manu:
A brāhmaṇa falls instantly through [selling] meat, lac, and salt;
and within three days a brāhmaṇa who sells milk becomes a śūdra.