Shiva Purana
इन्दुरेखासमाकारं तारारूपमथापि वा ॥ नीवारशूकस्सदृशं बिससुत्राभमेव वा ॥ ७२ ॥
It may be in the shape of a rainbow or in the form of a star. It may resemble a nyvara snake or resemble a seed thread.
english translation
indurekhAsamAkAraM tArArUpamathApi vA ॥ nIvArazUkassadRzaM bisasutrAbhameva vA ॥ 72 ॥
hk transliteration by Sanscript