Brihat Samhita
के चिदनन्तकुलौरगनिःश्वासौद्भूतं आहुराचार्याः । तद्यायिनां नृपाणां अभिमुखं अजयऽवहं भवति ॥ ३५-०२ ॥
In the opinion of certain writers the rainbow (indrāyudha) is formed of the expired breath of certain serpents of the divine order; princes that march out for fight in the direction of the rainbow will suffer defeat.
english translation
ke cidanantakulauraganiHzvAsaudbhUtaM AhurAcAryAH । tadyAyinAM nRpANAM abhimukhaM ajaya'vahaM bhavati ॥ 35-02 ॥
hk transliteration by Sanscript