Madhvaon Brahma Sūtra 1.3.38

For the Sudra is prohibited (from the study of the Vedas) as in the Gautama Dharma Sastra, “ The ears of him (the Sudra) who hears the Veda are to be filled with molten lead and lac, his tongue is to be slit if he pro- nounces it, his heart is to be cut open, if he attempts to know its meaning.” And Smriti says, “ the Sudra has no (consecrated) fire (to be maintained), no sacrifices (to be performed) ; so possibly he could not study the Vedas > however, free service to the three higher classes is prescribed for the Sudra, as the means of higher life.” But in the case of Vidura and others, as having already received the light of wisdom, some speciality is to be understood. From the text, “ all this visible and known world that having proceeded from Prana stands on it, trembles at the awful, formidable and energetic Vajra, knowing whom they become immortal,” (Kath. VI. 2), it appears that salvation results from the knowledge of the energetic Vajra (thunderbolt). To clear this doubt the Sutrakara has said: Btntei-sttASttfi.