Rishyasringa (Sanskrit: ऋष्यशृङ्ग; IAST: Ṛṣyaśṛṅga; Pali: Isisiṅga) is a rishi mentioned in Hindu and Buddhist scriptures from the late first millennium BCE. According to the Hindu epics Ramayana and Mahabharata, he was a boy born with the horns of a deer who became a seer and was lured by royal courtesans, which led to the yajna (fire sacrifice) of King Dasharatha. His story also occurs in the Buddhist Jatakas, where he is mentioned as the son of Bodhisatta and was tried to be seduced by royal courtesans.

The story of Rishyasringa briefly appears in the Ramayana, while a detailed account is narrated in the Mahabharata.

According to the Mahabharata, Vibhandaka, a renowned sage and a son of Kashyapa, travels in Mahahrada, when he sees Urvashi, the most beautiful apsara (nymph). Aroused, he emits his seed, which fell into the river. A doe, who is a cursed apsara, swallows it and becomes pregnant due to the sage's miraculous powers. After she gives birth to a boy, she is liberated from the curse and returns to heaven. The boy is born with horns and because of which, he is named Rishyasringa. Vibhandaka decides to raise him isolated from society. Rishyasringa grows up in his father's ashram in the forest, unaware of existence of any female. He practices brahmacharya and acquires magical and miraculous powers due to his chastity.

Meanwhile, Romapada—the King of Anga—offends a Brahmin, due to which no other Brahmin agrees to perform yajna (fire-sacrifice). This upsets Indra, the king of the gods, and he stops raining on Anga. As a result, the kingdom suffers from drought and famine. Romapada is told that the only way to bring rainfall is by bringing a man with perfect chastity into the kingdom. Romapada learns of Rishyasringa and despite his fear of the power and anger of Vibhandaka, he sends some courtesans to Rishyasringa to bring him into his kingdom.

During Vibhandaka's absence, the women come to his ashram and meet Rishyasringa. They tell him that they were hermits. Rishyasringa becomes astonished by seeing their appearance and invites them to perform tapas (penance) with him. Before Vibhandaka arrives, the women leave the place. Rishyasringa becomes love-sick and ignores his daily duties. The next day, the courtesans return and take Rishyasringa to Anga. As a result, the kingdom receives bountiful rains and Rishyasringa marries Shanta. Much of the story is taken up by accounts of the feelings of the young man as he becomes aware of women for the first time.

The story can be found in both the Ramayana and the Mahabharata. According to the Ramayana, Rishyasringa was the chief priest when the King Dasharatha performed a yajna to beget progeny, and Rama, Bharata, and the twins Lakshmana and Shatrughna were born.

The Naḷinikā Jātaka (Jā 526) introduces a past life of the Buddha, a sage, living alone in the Himālayas. There is semen in the urine he passes, a doe who eats the grass in that place gets pregnant from it. A human boy named Isisiṅga (Pali) is later born to the deer and he grows up in complete seclusion from mankind, and most importantly, from womankind. He even doesn't know the difference in the body and appearance of the two.

The boy's ascetic power becomes so great that it disturbs the god Sakka, the lord of heaven, who causes a drought to occur in the country and blames it on the boy. He then convinces the King to send his daughter to seduce him and to break the austerity of the young seer and to reduce his ascetic power. The King and his daughter accept Sakka's reasoning and in good faith – and for the benefit of the country – agree to be part of the plot.