Muchukunda, son of King Mandhata, was born in the Ikshvaku dynasty. Ikshvaku dynasty is also known as Suryavamsha. The important kings of this dynasty are Harishchandra, Dileepa, Raghu and Sri Rama.
Battle with the Asuras
Once, in a battle, the deities were defeated by the demons. Tormented by arrows, they sought help from king Muchukunda. King Muchukunda agreed to help them and fought against the demons for a long time. Since the deities did not have an able commander, king Muchukunda protected them against the demonic onslaught, until the deities got an able commander like Kartikeya, the son of Lord Shiva. Then Indra said to the king Muchukunda, "O king, we, the deities are indebted to you for the help and protection which you have given us, by sacrificing your own family life. Here in the heaven, one year equals three hundred and sixty years of the earth. Since, it has been a long time, there is no sign of your kingdom and family because it has been destroyed with the passage of time. We are happy and pleased with you, so ask for any boon except Moksha(liberation) because Moksha(liberation) is beyond our capacities".
Muchkunda asks Indra for a boon to sleep. While fighting on the side of the deities, king Muchukunda did not get an opportunity to sleep even for a moment. Now, since his responsibilities were over, overcome by tiredness, he was feeling very sleepy. So, he said, "O King of the deities, I want to sleep. Anyone who dares to disturb my sleep should get burnt to ashes immediately".
Indra said, "So be it, go to the earth and enjoy your sleep, one who awakens you would be reduced to ashes".
After this, king Muchukunda descended to earth and selected a cave, where he could sleep without being disturbed.
Kalayavan was undefeated and unmatched in battle due to a boon, but he was also merciless and cruel. He learns that Krishna is the only person who can defeat him in battle and accepting this challenge sets out to invade Krishna's kingdom, Mathura. When the two armies faced each other in battle, Krishna dismounts from his chariot and starts walking away, followed by Kalayavan. After a long time Krishna, followed by Kalayavan, enters a dark cave. In this cave Muchukunda was sleeping since the time he was blessed by king of deities.
The person on whom Muchkunda's gaze falls is doomed to instantaneous death. Kalayavan in a fit of anger and unable to see in the dark attacks Muchukunda mistaking him to be Krishna. When Muchkunda opens his eyes, his gaze falls on Kalayavan who is immediately burnt to death.
According to Hinduism, Muchukunda was an ancestor of Sri Rama, who belonged to Tretha Yuga. Sri Krishna appears towards the end of Dwapara Yuga. So, Muchukunda is asleep for a long time. After he woke up, he saw Sri Krishna and was delighted. Sri Krishna advised him to perform Tapas to cleanse the accumulated sins. Sri Krishna told him that his next life would be his last life. After that, he would get Moksha (liberation). Then, Muchukunda came out of the cave. He was astonished to see the size of various beings. The size of all creatures had shrunken due to evolution during the longtime that he was alseep. Then Muchukunda went to north to Gandamadana Mountain and from there to Badrika Ashrama.
The Muchkunda river i.e.Musi River is a tributary of Krishna River in the Deccan Plateau region of Telangana state in India. It originates in Ananthagiri Hills of Rangareddy dist, the hills where Muchukunda had his long sleep.So, the river gets the name as that. It flows through a major portion of Hyderabad, India and divides the historic old city with the new city. It was known as Muchukunda river in olden days, this name was changed to Musi,which name is still in use today. The reason for change of original name "Muchukunda" is not known. 
- Kashiyatra charitra - Enugula Viraswamayya (Telugu)