In Mahabhārata, Pratyūṣa was one of the Aṣṭavasu. Sage Devala was the son of Pratyūṣa, And Devala had two sons, great and merciful–

pratyūṣasya viduḥ putramṛṣiṃ nāmnātha devalam

dvau putrau  devalasyāpi kṣamāvantau manasvinau.

In Mahābhārata and Purāṇa(s), in most places, Asita and Devala have been mentioned together, though their separate identities can be recognised.

In the very beginning of Mahābhārata, we hear from Ugraśravā Sauti that Nārada chanted this million-verse Mahābhārata to the gods and Asita-Devala chanted it to the forefathers–

eka-śata-sahasrantu mānuṣeṣu pratiṣṭhitam

nārado̍śrāvayoddevān   asito devalo pitṛn.

From this śloka it appears that Asita is the adjective of Devala, just as in the ‘sarpasatra’ of Janamejaya, Asita and Devala are identified as one. Moreover, while describing the court of Brahmā in front of Yudhiṣṭhira, Asita and Devala become one, in a noun-adjective relationship–
asito-devalaścaiva nāradaḥ parvatastathā. Again, asito-devalaścaiva jaigīṣavyaśca tatvavit.

Before identifying Asita-Devala as on sage-personality, it needs to be known that in Tāṇḍya Mahābrāhmaṇa, or Pañcaviṃśa Brāhmaṇa, sage Asita is named as the son of Devala. One Sāma-mantra is referred to as āsita, that is, ̍uttered by Asita̍. Immediately after this, it is said that ̍Asita Daivalya̍, that is ̍Asita, son of Devala̍ was able to see what was going on in the three realms, by the power of his self-visualised mantra. This ̍āsita sāma̍ is applied for the fulfilment of the three hopes of human life.

It is to be noted that in Sabhāparva of Mahābhārata, where Dhaumya and Vyāsa , in front of Asita and Devala, performs the Abhiṣeka of Yudhiṣṭhira, in one version of Mahābhārata, Devala is referred to as ̍ Āsita̍, using taddhita-pratyaya, as the son of Devala–
nāradaṃ ca puraṣkṛtya devalaṃ cāsitaṃ munim.

Elsewhere in Mahābhārata, in the dicing episode, when Śakuni is insisting Yudhiṣṭhira for playing, Yudhiṣṭhira takes the name of Asita-Devala and says, sage Asita-Devala is learned, who has been able to have control over the sense-organs–
evamāhāyamasita devalo munisattamaḥ.

Here also, some would like to take the reading as ̍Āsita̍. Later we shall discuss, whether Asita and Devala are the same person or they are different.

Once in Vāyupurāṇa it has been said that Asita a sage belonging to the clan of Kaśyapa, and along with Devala, he is also one of the sages who have composed 9actually visualised) mantra(s)–
ete mantrakṛtaḥ sarve kāśyapāṃśca nivodhata.

In Vāyupurāṇa, it has also been said that two others girls, called Ekaparṇā and Ekapāṭalā, along with Umā, were born to Himālaya and Menā. Ekaparṇa was married to sage Asita–
asitasyaikaparṇā tu patnī sādhvī dṛḍhavratā

Devala was born out of the conception of Asita, and of the womb of Ekaparṇā–
devalaṃ suṣuve sā tu brahmiṣṭhaṃ mānasaṃ sutam.

So, in Vāyupurāṇa Asita is the father of Devala. In Brahmāṇḍapurāṇa, he has been called the greatest among the men elonging to Śāṇḍilya gotra, and he is one dedicated to the knowledge of Brahman.

The gotras of Asita , Devala and Kaśyapa have been integrated so that the descendants of them cannot marry among themselves.

In most of the places in Mahābhārata, Asita and Devala are mentioned together as ̍Asita-Devala̍. On a holistic consideration, it appears that Asita and Devala are the same person. In Śalyaparva of Mahābhārata, while speaking of the Āditya-tīrtha and in the context of the conversation between sage Asita- Devala and sage Jaigīṣavya.
Before going into the legend of Asita-Devala and Jaigīṣavya, it has been said in the prelude that– sage Asita-Devala, too, achieved the highest level of siddhi, in this site of pilgrimage.

asito devalaścaiva tasminneva mahātapāḥ
paramaṃ yogamāsthāya ṛṣiryogamavāptavān.

Not only in this śloka, wherever in Mahābhārata we have the mention of Asita-Devala together, there is no use of dvandva-samāsa or dvivacana. So wherever comes the name of Asita, it also means the presence of Devala. In this legend of Mahābhārata, the great-souled Asita-Devala was living in Āditya-tīrtha. He was always dedicated to the righteous path, and he performed tapasya, maintaing control over his senses, his outlook was equal to everything–
kāñchane loṣṭrabhāre ca samadarśī mahātapaḥ

Asita-Devala was very hospitable to brāhmaṇa(s), gods and guests, so one day sage Jaigīṣavya ame to his hermitage in Āditya-tīrtha.