The earliest Buddhist literature which deal with the stories of the various birth of Buddha are

The Jatakas are a collection of stories recounting the previous births of Gautama Buddha before he attained enlightenment [t4][t7]. These tales describe the Buddha's deeds in various forms, such as a human or an animal, while he was a Bodhisattva [c3][t5]. The Jatakas are considered part of the earliest Buddhist literature, with legends dating back to at least 380 BCE [t1][t6]. Specifically, they are categorized as the tenth book of the Khuddaka Nikaya within the Sutta Pitaka [t2][t5]. While the Vinaya Pitaka focuses on monastic rules and the Abhidhamma Pitaka on philosophical matters, the Jatakas serve as moral tales and religious literature accessible to ordinary people [c1][c2][t9]. They were often used as teaching aids and are frequently depicted in ancient Buddhist art at sites like Sanchi and Bharhut [t5][t6].

Sources

1. [1] History , class XI (Tamilnadu state board 2024 ed.) > Chapter 3: Rise of Territorial Kingdoms and New Religious Sects > The Starving Tigress: A Jataka Tale > p. 43
2. [2] https://ignca.gov.in/Asi_data/5753.pdf
3. [3] https://ignca.gov.in/coilnet/jatakint.htm
4. [4] THEMES IN INDIAN HISTORY PART I, History CLASS XII (NCERT 2025 ed.) > Chapter 4: Thinkers, Beliefs and Buildings > How Buddhist texts were prepared and preserved > p. 86