According to some Purāṇas (Puranas), all but four of the sixty thousand sons born of King Sagara’s first wife perished by the fire of Sage Kapila’s wrath. Pañcajana (Panchajana)(Pañcavana or Panchabana according to Vāyupurāṇa or Vayupurana) was one of the sons of King Sagara who survived. Śivapuraṇa (Shivapurana) states that Pañcajana became king after Sagara. Aṃśumāna (Angshuman) was Pañcajana’s son. But Harivaṃśapuraṇa (Harivangshapurana) has clearly mentioned that it was King Sagara’s son Asamañja (Asamanja) who later came to be known as Pañcajana. This Pañcajana-Asamañja became king after Sagara and was the father of Aṃśumāna — ekaḥ pañcajano nāma putro rājā vabhūva ha/ sutaḥ pañcajanasyāsīdaṃśumān nāma vīryavān.

According to Mahābhārata (Mahabharata), Aṃśumāna is clearly the grandson of King Sagara and the son of King Asamañja— aṃśumantaṃ samāhūya asamañjasutaṃ tadā/ pautraṃ bharataśārdūla idaṃ vacanamavravīt.

Sagara’s son Asamañja was extremely ill-behaved. Unable to put up with Asamañja‘s tyranny, the king’s subjects approached Sagara with grievances against his son. Enraged, Sagara banished Asamañja from the kingdom. As a result, Sagara’s grandson Aṃśumāna became the next king— pautre bhāraṃ samāveśya jagāma tridivaṃ tadā.

• Once, when King Sagara performed the Aśvamedha (Ashwamedha) yajña (yajna), his grandson Aṃśumāna was given the responsibility of protecting the sacrificial horse. Aṃśumāna, owing to his amicable nature, had become a favorite among the subjects and citizens from an early age. As directed by King Sagara, Aṃśumāna travelled to different kingdoms with the horse under his protection. With the ritual nearing its end, it was time to turn the horse around. On the other hand, envious of King Sagara’s sacred deeds, Indra abducted the sacrificial horse. The king’s high priest and spiritual preceptors advised him to retrieve the horse by all means before the yajña came to an end. King Sagara sent out his sixty thousand sons to look for the sacrificial horse and remained at the site of the yajña himself along with his grandson Aṃśumāna.

King Sagara’s sixty thousand sons looked far and wide and left no stone unturned in their search for the sacrificial horse. In the end, they started digging up the Earth in the hope of finding the horse. As they continued digging, they came upon the sage Kapila. The sacrificial horse was pacing close to the sage, who sat in a meditative state. When Sagara’s sons saw this, they accused Kapila to be the thief. This enraged the sage, who cried out in anger and burned them to ash.

When King Sagara saw that his sixty thousand sons showed no signs of returning, he gave his grandson Aṃśumāna the task to look for the sacrificial horse and also his sons who were like fathers in relation to Aṃśumāna.

According to the description in Mahābhārata, Aṃśumāna was initially not put in charge of the horse. It was only after Sagara’s sixty thousand sons had been burned to ash by Sage Kapila’s fire of rage that he summoned Aṃśumāna, the son of his exiled son Asamaṅja, and gave him the task of retrieving the sacrificial horse.

• Aṃśumāna dressed himself in warrior’s armour and followed the trail left by his uncles; he reached pātāla (patal; the netherworld). On his way, he came across the deity presiding over that particular quarter of the globe (dikpāla; dikpala) and the elephant assigned to protect it (diggaja). They assured Aṃśumāna that he would get back the sacrificial horse and blessed him aplenty. Following their directions  Aṃśumāna finally reached the place where his uncles were turned to ashes.

Aṃśumāna wept profusely at the sight of the spot where his uncles were burned. At the same time, he also noticed the horse which Indra’s magic had caused to disappear. Aṃśumāna was somewhat assured that his quest had ended and started looking for water to offer oblations to his deceased uncles. However, he could not find a water body anywhere. At that moment, he chanced upon his uncles’ maternal uncle and the lord of the birds, Suparṇa. It was Suparṇa who informed Aṃśumāna that his uncles had been charred to ashes by the curse of Sage Kapila. Their souls would not rest in peace if offered oblations with the water from any ordinary water body. It was only proper to offer prayers to them with the water of Gaṅgā (Ganga), the eldest daughter of Himālaya (Himalaya). The sons of King Sagara would rest in heaven only if Gaṅgā were to flow over the place where they had been turned to ashes.

According to an alternative version, Aṃśumāna met Sage Kapila himself. Mahābhārata relates that a heartbroken Aṃśumāna, on his grandfather Sagara’s command, arrived at the spot where his uncles had dug up the ground— jagāma duḥkhāttaṃ deśaṃ yatra vaidāritā mahī.

Aṃśumāna followed this path into the oceans, where he came across Kapila, who resembled a radiant sphere of energy; here he found the sacrificial horse as well. At first Aṃśumāna prayed to Kapila requesting him to return the horse to him, so that the yajña could be completed. He then asked for some holy water from the sage so that the souls of his uncles could be put to rest – sa vavre turagaṃ tatra prathamaṃ yajñakāraṇāt/ dvitīyamudakaṃ vavre pitṛnaṃ pāvanecchayā.

Pleased by Aṃśumāna’s modesty and fervent prayer, Kapila advised him to summon Gaṅgā, the savior of the fallen, to the spot where his uncles had been burned to ash so that their souls could find peace. King Sagara came to know about the entire episode from Aṃśumāna. He crowned Aṃśumāna the king and left the kingdom to perform religious austerities so that Gaṅgā could be brought down to earth. Aṃśumāna, too, at a later age, crowned his son Dilīpa the king, and left to spend his time in meditation so that Gaṅgā would flow on earth. However, he was not successful in his efforts to guide Gaṅgā down.

The accounts in Rāmāyaṇa (Ramayana) chronicle that Aṃśumāna, as advised by Suparṇa, returned his grandfather Sagara with the sacrificial horse. Sagara, upon hearing the entire report, went on to complete the yajña with a heavy heart. However, he was unable to find a way of bringing Gaṅgā to earth during his entire reign. Eventually, Aṃśumāna’s son Dilīpa ascended to the throne and Aṃśumāna dedicated himself to religious austerities for the purpose of ushering Gaṅgā. Aṃśumāna breathed his last while meditating. According to a different opinion, Sage Kapila himself had given Aṃśumāna the boon that it would be his grandson, that is Dilīpa’s son Bhagīratha, who would finally succeed in bringing Gangā to earth. Dilīpa apprised his son of this wish of his grandfather Aṃśumāna. 

It is only from Matsyapurāṇa (Matsyapurana) that we come to know that Aṃśumāna was married to Yaṣodā, the daughter born out of the wish of Haviṣmanta fathers. Aṃśumāna’s son Dilīpa was conceived by Yaṣodā.