"The Vedic literatures are divided into two parts: the srutis and the smrtis. The srutis are the four Vedas: Rg, Sama, Atharva and Yajur, and the Upanisads, and the smrtis are the Puranas like the Mahabharata, which includes Bhagavad-gita. The conclusion of all these is that one should know Sri Krsna as the Supreme Personality of Godhead."
Krsna Book, Chapter 87
"In the Bhagavad-gita you will find that vedais ca sarvair aham eva vedyah. Sarvam vedam: "all Vedas." "All Vedas" means originally there was one Veda, Rg Veda, or, somebody says, Atharva Veda. Then, later on it was divided into four: Rg, Sama, Yajur, Atharva. Then, from the Vedic injunction, then it was summarized, which is called Vedanta, summarized in sutras. Janmady asya yatah, athato brahma-jijnasa. In the sutra there are so many meanings. Then the Upanisads, 108 Upanisads, they are also Vedic. Then they were explained further for ordinary men--the Puranas. They are also Vedas. Then it was further explained by Mahabharata. So that is also Veda. Ramayana, that is also Veda. So any scripture, any literature, transcendental literature, whose aim is to understand God, that is Veda."
Srila Prabhupada Lecture on Srimad-Bhagavatam, 12-22-70, Surat
"Originally there was only one Veda, and there was no necessity of reading it. People were so intelligent and had such sharp memories that by once hearing from the lips of the spiritual master they would understand. They would immediately grasp the whole purport. But five thousand years ago Vyasadeva put the Vedas in writing for the people in this age, Kali-yuga. He knew that eventually the people would be short-lived, their memories would be very poor, and their intelligence would not be very sharp. "Therefore, let me teach this Vedic knowledge in writing." He divided the Vedas into four: Rg, Sama, Atharva and Yajur. Then he gave the charge of these Vedas to his different disciples. He then thought of the less intelligent class of men--stri, sudra and dvija-bandhu. He considered the woman class and sudra class (worker class) and dvija-bandhu. Dvija-bandhu refers to those who are born in a high family but who are not properly qualified. A man who is born in the family of a brahmana but is not qualified as a brahmana is called dvija-bandhu. For these persons he compiled the Mahabharata, called the history of India, and the eighteen Puranas. These are all part of the Vedic literature: the Puranas, the Mahabharata, the four Vedas and the Upanisads. The Upanisads are part of the Vedas. Then Vyasadeva summarized all Vedic knowledge for scholars and philosophers in what is called the Vedanta-sutra. This is the last word of the Vedas.
Vyasadeva personally wrote the Vedanta-sutra under the instructions of Narada, his Guru Maharaja (spiritual master), but still he was not satisfied. That is a long story, described in Srimad-Bhagavatam. Vedavyasa was not very satisfied even after compiling many Puranas and Upanisads, and even after writing the Vedanta-sutra. Then his spiritual master, Narada, instructed him, "You explain the Vedanta-sutra." Vedanta means "ultimate knowledge," and the ultimate knowledge is Krsna."
Sri Isopanisad, Introductin
"The Lord then began to speak on Vedanta philosophy as follows: Vedanta-sutra is spoken by the Supreme Lord Himself. The Supreme Lord, in His incarnation as Vyasadeva, has compiled this great philosophical treatise. Since Vyasadeva is an incarnation of the Supreme Lord, he cannot be likened to an ordinary person, who has the four defects which arise due to contact with material existence. The defects of a conditioned soul are: (1) he must commit mistakes; (2) he must be illusioned; (3) he must possess the tendency to cheat others; and (4) all his senses must be imperfect. We must understand that the incarnation of God is transcendental to all these defects. Thus whatever has been spoken and written by Vyasadeva is considered to be perfect. The Upanisads and Vedanta-sutra aim at the same goal: the Supreme Absolute Truth. When we accept the import of Vedanta-sutra and the Upanisads directly as they are stated, we become glorified. The commentaries made by Sankaracarya, however, are indirect and are very dangerous for the common man to read, for by understanding the import of the Upanisads in such an indirect, disruptive way, one practically bars himself from spiritual realization.
According to the Skanda and Vayu Puranas, the word sutra refers to a condensed work which carries meaning and import of immeasurable strength without mistake or fault. The word vedanta means "the end of Vedic knowledge." In other words, any book which deals with the subject matter indicated by all the Vedas is called Vedanta. For example, Bhagavad-gita is Vedanta because in Bhagavad-gita the Lord says that the ultimate goal of all Vedic research is Krsna. Thus Bhagavad-gita and Srimad-Bhagavatam, which aim only at Krsna, are to be understood to be Vedanta.
....From Vedic literatures we understand that the Vedas originated from the breathing of Narayana. Vyasadeva, who is an incarnation of the power of Narayana, has compiled the Vedanta-sutra (nyaya-prasthana), but according to Sankara's commentaries, Apantaratama Rsi is also accredited with having compiled the codes of Vedanta-sutra. According to Lord Caitanya, the codes of the Pancaratra and the codes of Vedanta are one and the same. Since the Vedanta-sutra is compiled by Vyasadeva, it should be understood to be spoken by Narayana Himself. From all descriptive literatures dealing with Vedanta-sutra, it appears that there were many other rsis contemporary with Vyasadeva who also discussed Vedanta-sutra. These sages were Atreya, Asmarathya, Audulomi, Karsnajini, Kasakrtsna, Jaimini, Badari and other sages such as Parasari and Karmandi."
Teachings of Lord Caitanya, Chapter 19
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.
Srimad-Bhagavatam (the summary explanation of the four Vedas), composed by Rishiraj Vyas Muni, the compiler of the Vedas, is 18,000 verses long. Padma Purana is 400,000 verses long. There are four Vedas, 108 Upanishads, 18 primary puranas, and 18 upa-puranas for each primary purana. There are upa-puranas, Itihasas, tantras, samhitas, upa-samhitas, and thousands of other sruti and smriti texts; and there are myriad books, compositions, and commentaries by the acharyas. The texts of the Vedas are known as Samhitas, and within the Samhitas there are Mantras, which are prayers in the form of potent sound vibrations that were revealed to advanced devotees for different purposes. In the Vedic civilization three orders of life lived in the forests. Only grhasthas inhabited the cities. The regulated knowledge for living in the city, is revealed in the books known as Brahmanas, whereas the regulated knowledge for living in the forest is revealed in the books known as Aranyakas.