Satya and Dasra, two sons of Surya are called Ashwinikumaras, as per Mahabharata Anushasanaparva Chapter 150 verse 17-18. They’re also called Ashwi or Ashwis or Ashwinidevas and are divine physicians as per Mahabharata Aranyaparva Chapter 123 verse 12.

Antecedents: Vishnu – Brahma – Marichi – Kashyapa – Vivasvan (Surya) – Ashwinis.

As per the Vishnupurana, Vishwakarma’s daughter Samjna was Surya’s wife. They had three children – Manu, Yama, Yami. Once Samjna was oppressed by Surya’s brilliance and gave the duty of looking after him to Chaya and left for the forests. Surya mistook Chaya for Samjna and had 3 children with her too – Shanaishchara, another Manu and Tapati. Surya understood his mistake only when Chaya once cursed Yama. With his divine sight, Surya understood that Samjna was meditating in the form of a horse. Surya also assumed the form of a horse and thus was born the Ashwinis and Revanta. He then took her back, as per Vishnupurana Ansh 3 Chapter 2. According to Mahabharata Adiparva Chapter 66 verse 35, the Ashwinis were born from Samjna’s nostrils.

Sharyati, the son of Vaivasvatamanu, had 4000 beautiful wives, but he was childless. While he was beginning to get worried, one of his wives gave birth to a girl. She was named Sukanya and the king and his wives showered her with affection. In Sharyati’s kingdom, there was a garden as beautiful as Nandavana and a lake equal to Manasarovar. In one part of the garden, the sage Chyavana meditated. He had given up food and water and had been meditating for several years. In time, he became covered with creepers, anthills, and even birds’ nests. Chyavana was oblivious to all this. Once Sharyati, his wives and Sukanya visited the garden. The king and queens started enjoying themselves in the lake, while Sukanya wandered away with a few maids. They reached the place where Chyavana was meditating and Sukanya saw something glimmering in the mound. She took a stick and started poking at the mound to find out what was inside. The sage became conscious of this and asked the girl to let him meditate in peace. Sukanya was irritated that the sage should speak this way to the king’s daughter. Out of spite, she blinded the sage using the stick, and left the place. The sage was in a lot of pain, and was angry too, but was patient enough not to curse the princess. But soon after, bad omens started appearing all over the kingdom, and people started suffering from diseases. They complained to the king, who was trying to understand what was going wrong. Soon he began to wonder if someone had harmed the great sage who meditated in the garden in his kingdom. Though the king continued his investigation he didn’t manage to find anything. Finally, seeing her father and the kingdom in trouble, Sukanya told her father what had happened, though she claimed it was an accident. The king rushed to the garden, prostrated in front of the sage, and begged for his forgiveness. The sage agreed, provided Sukanya was given to him in marriage.

The king was now in a fix because he didn’t want his daughter married off to the old sage, but Sukanya told him that she was fine with marrying the sage. Thus Chyavana was married to Sukanya. Sukanya served her husband well and ensured that all his needs were taken care of. Once, the Ashwinis happened to visit the area, and saw Sukanya returning from the lake after her bath. They were dazzled by her beauty, and asked her who she was and what she was doing in the jungle. Sukanya told them that she was Sharyati’s daughter and had become Chyavana’s wife due to certain events. She said that she lived with the old sage in the hermitage nearby. She also invited them to the hermitage. The Ashwinis, on hearing this, said that she was worthy of a husband better than Chyavana, and she could marry either of them. Sukanya didn’t like this, and told them that she would curse them if they continued in this vein. The Ashwinis were taken aback at her reaction and said she could ask them any boon she wished for. They said that since they were physicians, they could restore her husband’s eyesight, and make him as handsome as they were, but on one condition. The condition was that they would transform Chyavana to make him look exactly like them, and she would have to choose from the three of them who her husband would be. They asked Sukanya to decide. She was glad for her husband, but uncomfortable about the condition. She rushed to the hermitage, apprised her husband of the events, and asked him what she should do. Chyavana asked her not to worry further and to bring the Ashwinis to the hermitage. She did that, and the Ashwinis first asked Chyavana to take a bath in the lake. When he dipped into the water, the Ashwinis did so too, and when they resurfaced, all three of them looked the same. A voice asked Sukanya to choose. She started praying to the gods and a devi gave her the power to identify her husband. As per Devibhagavata Saptamaskanda, the Ashwinis were pleased with her devotion and blessed her.

Chyavana was thankful to the Ashwinis, and asked them to name a boon. They said that Indra had forbidden them from consuming soma for no reason at a yaga conducted by Brahma. They said that if he could, Chyavana should get them back the right to drink soma. Chyavana agreed.

Later, when Sharyati and his queen came to enquire about Sukanya, they were found the transformed Chyavana. They worried about their daughter’s fidelity, but were delighted on hearing about the events that transpired. Chyavana also told him about the Ashwinis’ problem, and he agreed to help them. After a few days, Sharyati and his wife bid goodbye to their daughter and son-in-law. In the next available auspicious time, the king started a yajna, invites Vasishta and other important sages and began the yajna under the leadership of Bhargava (Chyavana). All the devas arrived, looking for offerings. The Ashwinis were there too, much to the displeasure of Indra. He kept berating them until the time came for drinking soma. Chyavana offered it to the Ashwinis too, but Indra stopped him and said the Ashwinis were not allowed to drink it. As per Devibhagavata Saptamaskanda, Chyavana and Indra got into an argument which Chyavana won, and the Ashwinis got the soma.

See Aapodhaumyan for the story of how the Ashwinis tested Upamanyu.

Pandu’s wife Kunti got five boons from Durvasa. She used one of them while she was unmarried. She used three boons to summon Yama, Vayu and Indra to produce Yudhishtira, Bhima and Arjuna. She gave the remaining boon to Madri, Pandu’s other wife. She summoned the Ashwinis and later gave birth to Nakula and Sahadeva.

As per Mahabharata Adiparva Chapter 186 verse 6, the Ashwinis were present for Draupadi’s swayamwar. In the Khandava battle, they sided with Indra and fought Arjuna. A king called Yuvanasha became pregnant with his child Maandaata. The Ashwinis split the king’s stomach and brought the child out,a s per Mahabharata Dronaparva Chapter 62 verse 3.

According to Mahabharata Shalyaparva Chapter 43 verse 38, they gave attendants to Skanda. As per Mahabharata Anushasanaparva Chapter 65 verse 7, they like offerings of ghee. According to Mahabharata Anushasanaparva Chapter 65 verse 10, the Ashwina month is special to the Ashwinis and gifting ghee to brahmins during that time will make a person more beautiful. As per Mahabharata Anushasanaparva Chapter 107 verse 95, if ghee offered to agni is consumed for 12 months, a person can enter the world of the Ashwinis. As per Rigveda Sukta 93, the Ashwinis and Surya, Chandra are the same.

According to Rigveda Sukta 112 Rik 11, Deerkhashravas, son of Deerkhatamas once prayed to the Ashwinis to end a drought. As per Rigveda Sukta 116 Rik 9, a sage named Gomata once prayed to the Ashwinis when he was thirst in a desert. They appeared as a well and quenched it. A sage called Dadhyanga taught the Ashwinis the Madhuvidya. Dadhyanga was taught the mantra by Indra, who decreed that if he passed the information to anyone else, Indra would behead him. The Ashwinis replaced the sage’s head with that of a horse, and he taught them. Once they had learned it, they replaced the horse’s head with the sage’s own head, as per Rigveda Sukta 116 Rik 12.

The donkey is the Ashwinis’ vehicle. Once their donkey transformed into a wolf and approached Rijrashwa, the son of a rajarishi named Vrishagir. Rijrashwa gave it the meat from a hundred goats. Vrishagir wasn’t pleased with this. He cursed his son to blindness. Rijrashwa prayed to the Ashwinis and gained his eyesight back, as per Rigveda Sukta 115 Rik 16.

Once Surya decided to marry his daughter to one of the devas. He conducted a horse race and decreed that the winning horse’s owner would get his daughter. The Ashwinis’ horse won the race and they were married to Surya’s daughter as per Rigveda Sukta 117 rik 17.

The Ashwinis destroyed the entire family of an asura named Vishwak, as per Rigveda Sukta 11 rik 16.