If one engages in the service of a Shudra, he is doomed to perdition though he may duly perform all the rites of his caste. A Brahmana a Kshatriya or a Vaishya, so engaging is doomed although given to the proper performance of religious rites.
शूद्रस्य कर्मनिष्ठायां विकर्मस्थोऽपि पच्यते। ब्राह्मणः क्षत्रियो वैश्यो विकर्मस्थश्च पच्यते॥