Brihat Samhita
शक्रचापपरिघप्रतिसूर्या रोहितो अथ तडितः परिवेषः । उद्गमास्तमये यदि भानोरादिशेत्प्रचुरं अम्बु तदाशु ॥ २८-१६ ॥
If at the time of sunrise or sunset, there should be seen in the sky the rainbow, clouds rod-like in shape, the mock-Sun or the appearance known as Rohita (straight rainbow), or lightning or halo, there will be abundance of immediate rain.
english translation
zakracApaparighapratisUryA rohito atha taDitaH pariveSaH । udgamAstamaye yadi bhAnorAdizetpracuraM ambu tadAzu ॥ 28-16 ॥
hk transliteration by Sanscript