The notion of a fifth veda (Sanskrit

Sanskrit

Sanskrit , is a historical Indo-Aryan language and the primary liturgical language of Hinduism, Jainism and Buddhism.Buddhism: besides Pali, see Buddhist Hybrid Sanskrit Today, it is listed as one of the 22 scheduled languages of India and is an official language of the state of Uttarakhand...

: ), that is, of a text which lies outside than the four canonical Vedas but nonetheless has the status of a Veda, is one that has been advanced in a number of post-Vedic Hindu texts, in order to accord a particular text or texts and their doctrines with the timelessness and authority that Hinduism

Hinduism

Hinduism is the predominant and indigenous religious tradition of the Indian Subcontinent. Hinduism is known to its followers as , amongst many other expressions...

 associates with the Vedas. The idea is an ancient one, appearing for the first time in the Upanishad

Upanishad

The Upanishads are philosophical texts considered to be an early source of Hindu religion. More than 200 are known, of which the first dozen or so, the oldest and most important, are variously referred to as the principal, main or old Upanishads...

s, but has over the centuries since then also been applied to more recent Sanskrit and vernacular texts.
The earliest reference to a fifth veda is found in the Chandogya Upanishad

Chandogya Upanishad

The Chandogya Upanishad is one of the "primary" Upanishads. Together with the Jaiminiya Upanishad Brahmana and the Brihadaranyaka Upanishad it ranks among the oldest Upanishads, dating to the Vedic Brahmana period....

 (7.1.2), which applies the term to the "histories" (Itihasa

Itihasa

Itihasa as defined by Amarakosha refers to purvavritta, i.e. events of the past. In the Vedic age, those portions of the Brahmanas which narrated events of bygone days were known as itihasa and had some ritualistic importance...

-Purana, "ancient traditions") of its day,

This reference to itihasa was used by the Mahabharata

Mahabharata

The Mahabharata is one of the two major Sanskrit epics of ancient India and Nepal, the other being the Ramayana. The epic is part of itihasa....

, which belonged to the class of epic literature

Indian epic poetry

Indian epic poetry is the epic poetry written in the Indian subcontinent, traditionally called Kavya . The Ramayana and Mahabharata, originally composed in Sanskrit and translated thereafter into many other Indian languages, are some of the oldest surviving epic poems on earth and form part of...

 called "itihasa", to refer to itself as the fifth veda.