Shiva Purana
ब्राह्मणत्वं शुभं प्राप्य ब्राह्मण्यं योऽवमन्यते ॥ भोज्याभोज्यं न जानाति स पुमान्क्षत्रियो भवेत् ॥ ७ ॥
After attaining the auspicious brahminhood if a person disrespects brahminhood and does not differentiate between what could be eaten and what could not be eaten he becomes a Kṣatriya.
english translation
brAhmaNatvaM zubhaM prApya brAhmaNyaM yo'vamanyate ॥ bhojyAbhojyaM na jAnAti sa pumAnkSatriyo bhavet ॥ 7 ॥
hk transliteration by Sanscript