Śatapatha Brāhmaṇa ("of a hundred paths") 13.1.5.4

13.1.5.4

tadāhuḥ yadubhau divā gāyetām prabhraṃśukāsmācrīḥ syādbrahmaṇo vā etadrūpaṃ yadaharyadā vai rājā kāmayate'tha brāhmaṇaṃ jināti pāpīyāṃstu bhavati

Concerning this they say, ‘Were both to sing by day, his distinction would be apt to fall away from him: for that--to wit, the day--is a form of the priestly dignity; and when the king chooses he may oppress (despoil) the Brâhmana, but he will fare the worse (or, become the poorer) for it.