Shiva Purana
कर्मणा येन मेधावी शूद्रो वैश्यो हि जायते ॥ तत्ते वक्ष्यामि निखिलं येन वर्णोत्तमो भवेत् ॥ ८ ॥
I shall explain to you entirely that which gives a higher caste whereby an intelligent Śūdra becomes a Vaiśya.
english translation
karmaNA yena medhAvI zUdro vaizyo hi jAyate ॥ tatte vakSyAmi nikhilaM yena varNottamo bhavet ॥ 8 ॥
hk transliteration by Sanscript