Manava Dharmashastra 10.98

10.98

vaiśyo 'jīvan svadharmeṇa śūdravṛttyāpi vartayet
anācarann akāryāṇi nivarteta ca śaktimān //

A Vaisya who is unable to subsist by his own duties, may even maintain himself by a Sudra's mode of life, avoiding (however) acts forbidden (to him), and he should give it up, when he is able (to do so).