One day the chief of the celestials assuming a form of celestial beauty, came to the retreat of the Rishi, thinking that the opportunity he had been expecting had at last come. Verily, O king, having assumed a form unrivalled for comeliness and exceedingly tempting to women and highly agreeable to look at, Indra entered the ascetic's asylum. He saw the body of Vipula staying in a sitting posture, immovable as a stake, and with eyes destitute of vision, like a picture drawn on the canvas. And he saw also that Ruchi was seated there, adorned with eyes whose ends were extremely beautiful, possessed of full and rotund hips, and having a deep and swelling bosom. Her eyes were large and expansive like the petals of the lotus, and her face was as beautiful and sweet as the moon at full. Seeing Indra come in that guise, the lady wished to rise up and offer him a welcome. Her wonder having been excited at the unrivalled beauty of form which the person possessed, she very much wished to ask him as to who he was. Although, however, she wished to rise up and offer him a welcome, yet her limbs having been restrained by Vipula who was dwelling within her, she failed, O king, to do what she wished. In fact, she was unable to move from the place where she sat. The chief of the celestials then addressed her in agreeable words uttered with a sweet voice. Indeed, he said, 'O thou of sweet smiles, know that I am Indra, arrived here for thy sake! Know, O sweet lady, that I am afflicted by the deity of desire provoked by thoughts of thee! O thou of beautiful brows, I have come to thy presence. Time wears off.' 1These words that Indra spoke were heard by the ascetic Vipula. Remaining within the body of his preceptor's wife, he saw everything that occurred. The lady of faultless beauty, though she heard what Indra said, was, however, unable to rise up for welcoming or honouring the chief of the celestials. Her senses restrained by Vipula, she was unable to utter a word in reply. That scion of Bhrigu's race, of mighty energy, judging from the indications afforded by the body of his preceptor's wife that she was not unwilling to receive Indra with kindness, restrained her limbs and senses all the more effectually, O king, by his Yoga-powers. With Yoga-bonds he bound up all her senses. Beholding her seated without any indication of agitation on her person, the lord of Sachi, abashed a little, once more addressed that lady who was stupefied by the Yoga-powers of her husband's disciple, in these words, 'Come, come, O sweet lady!' Then the lady endeavoured to answer him. Vipula, however restrained the words that she intended to utter. The words, therefore, that actually escaped her lips (under the influence of Vipula) were. 'What is the reason of thy coming hither?' These words adorned with grammatical refinements, issued out of her mouth that was as beautiful as the moon. [paragraph continues] Subject to the influence of another, she uttered these words, but became rather ashamed for uttering them. Hearing her, Purandara became exceedingly cheerless. Observing that awkward result, the chief of the celestials, O monarch, adorned with a thousand eyes saw every thing with his spiritual eye. He then beheld the ascetic staying within the body of the lady. Indeed, the ascetic remained within the body of his preceptor's wife like an image or reflection on a mirror. Beholding the ascetic endued with the terrible might of penances, Purandara, O monarch, fearing the Rishi's curse, trembled in fright. Vipula then, possessed of high ascetic might, left the body of his preceptor's wife and returned to his own body that was lying near. He then addressed the terrified Indra in the following words: Vipula said, 'O wicked-souled Purandara, O thou of sinful mind, O wretch that hast no control over thy senses, neither the deities nor human beings will worship thee for any length of time! Hast thou forgotten it. O Sakra,--does it not still dwell in thy remembrance,--that Gautama had cursed thee in consequence of which thy body became disfigured with a thousand sex-marks, which, owing to the Rishi's compassion, were afterwards changed into organs of vision? I know that thou art of an exceedingly foolish understanding, that thy soul is uncleansed, and that thou art of an exceedingly unstable mind! O fool, know that this lady is being protected by me. O sinful wretch, go back to that place whence thou tamest. O thou of foolish soul, I do not consume thee today into ashes with my energy. Verily, I am filled with compassion for thee. It is for this that I do not, O Vasava, wish to burn thee. My preceptor, endued with great intelligence, is possessed of terrible might. With eyes blazing with wrath, he would, if he saw thee, have burnt thy sinful self today. Thou shouldst not, O Sakra, do like this again. The Brahmanas should be regarded by thee. See that thou dost not, with thy sons and counsellors, meet with destruction, afflicted by the might of the Brahmanas. Thou thinkest that thou art an immortal and that, therefore, art at liberty to proceed in this way. Do not, however, disregard the Brahmanas. Know that there is nothing unattainable by penance.'
There's more to the story, by the way. After Vipula protects Ruchi, he doesn't tell his Devasharma about how he went inside Ruchi. Vipula soon realizes that this is a sin with dire consequence in the afterlife, but the sin is removed after Devasharma forgives Vipula for not telling him. Then Devasharma, Ruchi, and Vipula all go to Swarga.