After Indra's penance to Shiva and Vishnu, as explained above-
तत्राभवच्छिवस्यैव गङ्गाविष्ण्वोः प्रसादतः॥ ९७ ॥
अम्भसा पुरुषो जातः शिवविष्णुस्वरूपधृक्।
चक्रपाणिः शूलधरः स गत्वा तु रसातलम्॥ ९८ ॥
निजघान तदा दैत्यमिन्द्रशत्रुं महाशनिम्।
सखाऽभवत्स चेन्द्रस्य अब्जकः स वृषाकपिः॥ ९९ ॥
Then by the blessings of Shiva, Ganga and Vishnu, a man born of water, appeared there.
He had form of both Shiva and Vishnu. In one hand he had Chakra, and Trishoola in the other hand, and going to the Rasaatala(a dimension of existence which exists under Earth), killed the Daitya MahaShani, the enemy of Indra.
He then became friends with Indra and became known as Abjaka and Vrishaakapi.
Problem in Indra's domestic life, due to misunderstanding of Shachi-
दिविस्थोऽपि सदा चेन्द्रस्तमन्वेति वृषाकपिम्।
कुपिता प्रणयेनाभूदन्यासक्तं विलोक्य तम्॥
शचीं तां सान्त्वयन्नाह शतमन्युर्हसन्निदम्॥ १०० ॥
Even after Indra was again established in the Heavens, He used to always visit Vrishaakapi.
This made Indraani contemptuous due to amorous affectionate infatuation, when She used to see Him go frequently and thought He is in love with someone else.
Then Shatamanyu Indra, consoling Her, tells Shachi smilingly this-
नाहमिन्द्राणि शरणमृते सख्युर्वृषाकपेः।
वारि वाऽपि हविर्यस्य अग्नेः प्रियकरं सदा॥ १०१ ॥
नाहमन्यत्र गन्ताऽस्मि प्रिये चाङ्गेन ते शपे।
तस्मान्नार्हसि मां वक्तुं शङ्कयाऽन्यत्र भामिनि॥ १०२ ॥
पतिव्रता प्रिया मे त्वं धर्मे मन्त्रे सहायिनी।
सापत्या च कुलीना च त्वत्तोऽन्या का प्रिया मम॥ १०३ ॥
तस्मात्तवोपदेशेन गङ्गां प्राप्य महानदीम्।
प्रसादाद्देवदेवस्य विष्णोर्वै चक्रपाणिनः॥ १०४ ॥
तथा शिवस्य देवस्य प्रसादाच्च वृषाकपेः।
जलोद्भवाच्च मे मित्रादब्जकाल्लोकविश्रुतात्॥ १०५ ॥
उत्तीर्णदुःखः सुभग इत इन्द्रोऽहमच्युतः।
Indra tells Shachi-
O Indraani! I do not go to anyone except for my friend Vrishaakapi. Water too always benefits Agni of Havish(Yagya). So do I also oath that I go to nowhere else other than Thee, O Beloved! Thus O my Lover! Thou art not to suspect me of going other places.
Thou art devoted to me, art my beloved, assistest me in Dharma and advicest me right things, Thou hast good progeny, art from good family, so who other than Thee is my beloved?
It is only by Thy advice I went to the great river Ganges, and got blessings of the Vishnu,Who holds Chakra in His hands and Who is Lord of Gods; and I got blessing of Lord Shiva. And by thier blessings my friend Vrishaakapi, Who is born of water and is renowned in all worlds as Abjaka, liberated me from my sorrows, and O Prosperous Shachi! now I am Indra again and will not fall from this position. It is all because of Thee.
Now Indra explains glories of Vishnu, Shiva and Ganga-
गङ्गायाः सदृशं नास्ति श्रुणु चान्यद्वरानने॥ १११ ॥
धर्मार्थकाममोक्षाणां प्राप्तये पापमुक्तये।
शिवविष्ण्वोरनन्यत्वज्ञानान्नास्त्यत्र मुक्तये॥ ११२ ॥
तस्मात्तव धिया साध्वि सर्वमेतन्मनोगतम्।
अवाप्तं च शिवाद्विष्णोर्गङ्गायाश्च प्रसादतः॥ ११३ ॥
इन्द्रत्वं मे स्थिरं चेतो मन्ये मित्रबालात्पुनः।
वृषाकपिर्मम सखा यो जातस्त्वप्सु भामिनि॥ ११४ ॥
त्वं च प्रियसखी नित्यं नान्यत्प्रियतरं मम।
O Beautiful-faced Shachi! listen, there is no other place like Gangaa which can confer Dharma, Artha, Kaama, Moksha, and liberate one from sins, and there is no other means of liberation other than the knowledge of non-difference between Shiva and Vishnu. This all things O Virtuous One! is to be established by Thee in Thy mind by Thy intelligence.
By the blessings of These very three Gods- Shiva, Vishnu and Ganga, that I thus attained again this stable position of Indra by the power of my friend.
O Beautiful Shachi! Vrishaakapi is my friend and He is born of water, and Thou also art always my beloved friend, and no one other than you two is beloved of me.
तीर्थानां गौतमी गङ्गा देवानां हरिशंकरौ॥ ११५ ॥
तस्मादेभ्यः प्रसादेन सर्वं चेप्सितमाप्तवान्।
मम प्रीतिकरं चेदं तीर्थं त्रैलोक्यविश्रुतम्॥ ११६ ॥
Gautami Gangaa is best of Teerthas(pilgrimage places) and Hari and Shankara are best of Gods. By grace of These, all desired things are obtained. So is this IndraTeertha renowned in the three worlds and is very dear to me.
[Note- this IndraTeertha is at bank of Ganges where all this episode of incarnation of Vrishaakapi happened. This Teertha is also called Abjaka and Vrishakapa, and Shiva, Indra, Vishnu, Ganga reside there. This is explained in the very chapter]
अत्र तु स्नानमात्रेण सर्वे ते मुक्तिमाप्नुयुः।
पापिष्ठाः पापतो मुक्तिमाप्नुयुर्ये च धर्मिणः॥ १२० ॥
तेषां तु परमा मुक्तिः पितृभिः पञ्चपञ्चभिः।
By mere bathing in this Teertha all get liberation. Even the best of sinners get freedom from sins, and those people who are religious they get the supreme state of liberation and are freed from the debt of forefathers(Pitri) and from the other five debts.