Shiva Purana
श्रुत्वा तद्वृत्तमाज्ञाय तं शशाप कृतागसम् ॥ अकामतोविचार्य्येति शूद्रो भव न क्षत्रियः ॥ ५८॥
On hearing about the incident and realising that he had committed a sin unconsciously and not wilfully, the preceptor cursed him—“Become a Śūdra, not a Kṣatriya.”
english translation
zrutvA tadvRttamAjJAya taM zazApa kRtAgasam ॥ akAmatovicAryyeti zUdro bhava na kSatriyaH ॥ 58॥
hk transliteration by Sanscript