Brihat Samhita
अहुताशे अनलरूपं यस्मिंस्तत्केतुरूपं एवौक्तम् । खद्योतपिशाचालयमणिरत्नऽदीन्परित्यज्य ॥ ११-०३ ॥
Ketus are luminous appearances resembling fíre but without the power to consume objects—the glow worm, certain phosphorescent appearances, gems, precious stones and the like excepted.
english translation
ahutAze analarUpaM yasmiMstatketurUpaM evauktam । khadyotapizAcAlayamaNiratna'dInparityajya ॥ 11-03 ॥
hk transliteration by Sanscript