Sarg 32 - Raavan Fights with Arjun 

"Hey Raam, where Raavan was worshipping Shankar Jee, Arjun was taking bath with his women at some distance from that place [down the river]. To test his strength, he just spread his 1,000 arms and stopped the water flow of Narmadaa river. Now its water overflowed the banks and flowed backward. Because of this backward flowing, Raavan's worshipping material for Shiv Jee also flowed in the water. Seeing this Raavan got very angry. He looked at Narmadaa's water. He was not supposed to speak [because he was still worshipping Shiv Jee], so he asked Shuk and Saaran to find out the reason of water flow upward by signs. Raakshas immediately went through skyway and found a very tall man playing with women in the water spreading his thousand arms at a distance of two Kos from the place Raavan was worshipping.

Seeing this they came back and said - "Hey Raajan, There is a man who has thousand arms. He is playing with women in Narmadaa spreading his thousand arms, and that is how the water is flowing upward." Hearing this Raavan immediately knew that this man was no other than Sahastraarjun. He immediately went there to fight with him. He asked Arjun's ministers to tell him that Raavan wanted to fight with him.

His ministers said - "You are completely fool. Our Raajaa is taking bath after drinking liquor. This is not the time to fight with him. If you want to fight with him, then come tomorrow, and if you want to fight now, then first fight with us." Raavan fought with them and killed them. Seeing this Arjun's men reported this to Arjun.

Arjun pacified the people and came out of the water. He took his Gadaa and attacked Raavan. Prahast attacked Arjun with the Moosal. Arjun picked his Gadaa with his 500 hands, and hit Prahast. Prahast fell down. Then Raavan came and they had a fierce fight. In the last Arjun caught Raavan with his thousand arms and roared loudly. Devtaa showered flowers on Arjun. Arjun took Raavan to the city.

Sarg 33 - Pulastya Muni Frees Raavan 

Hearing about Raavan's arrest, Pulastya Muni came to see his grandson. Seeing Muni coming on foot, Arjun's people informed Arjun. Arjun welcomed Muni very happily. He welcomed  Muni, worshipped him and said - "Hey Braahman, I feel blessed seeing your feet in my city. Mahishmatee Nagaree has become holy. Kindly order me, what can I do for you?" Muni asked Raaja's welfare and said - "Hey Raajaa, You have shown your bravery arresting our very mighty grandson with whose fear seas and wind stay stagnant where they are. Your glory is immortal because of winning Raavan, but Hey Putra, now you free Raavan because of me."

Arjun didn't consider proper to disobe Muni, so he immediately released Raavan. He made him wear divine clothes and jewelry, declared him his friend in front of Agni and put a condition that if Raavan will ask any help to trouble somebody he couldn't be able to help him."

Arjun bade farewell to Raavan. Embarrassed with defeat in fight, by embracing him, and being freed by Pulastya Rishi, Raavan came from there. After getting Raavan  freed, Pulastya Muni went to Brahm Lok. Thus there were some powerful kings also at that time.