Who developed the terminology of the Prasthanatrayi of the Vedanta school?

Question

The most popular school of Hindu philosophy is the Vedanta school. Vedanta derives its teachings from three sources or authorities, known as the Prasthanatrayi or three starting points:

1. The Upanishads, texts traditionally included with the Vedas consisting of conversations between sages and their students which clarify the philosophical teachings of the Vedas. In the Vedanta tradition they're referred to as the Shruti Prasthana, because the Vedas are Shruti or heard from the gods.

2. The Bhagavad Gita, which needs little introuction. This is referred to as the Smriti Prasthana, because the Bhagavad Gita is part of Mahabharata which is a Smriti text, as it was composed by the sage Vyasa.

3. The Brahma Sutras, AKA the Vedanta Sutras, a work by Vyasa which summarizes and systematizes the philosophical doctrines laid out in the Upanishads. It is referred to Nyaya Prasthana, because Vyasa relies on Nyaya or logic to argue for his interpretation of the words of the Upanishads. (You can read the Brahma Sutras here.)

My question is, who developed this terminology of calling these texts the Prasthanatrayi or three starting points of philosophical knowledge? Does Vyasa mention this in the Brahma Sutras? Or was it invented by subsequent Vedantic thinkers like Adi Shankaracharya?

This should go without saying, but just in case, I'm not looking for who are the author of these three. I'm asking who singled out these particular works as the three starting points of the Vedanta school.

Answer 1

Swami Vivekananda refers to the 3 pillars several times in his writings. One reference is Vol 3, p 327-328 of his Complete Works (lecture entitled "The Vedanta in All Its Phases"). But he refers to it as something being more or less already self-evident and never references a source.

He says "All these Darshanas that you have ever seen or heard are based upon Upanishadic authority...And as I have said, all the sects of India now hold these Vyasa-Sutras to be the greatest authority, and every new sect starts with a fresh commentary on the Vyasa-Sutras according to it's light...Next in authority is the celebrated Gita. The great glory of Shankaracharya was his preaching of the Gita...And he has been followed by the founders of the orthodox sects in India, each of whom has written a commentary on the Gita."

EDIT: I did some further research. The first reference I can find is a Vedanta philosopher named Sadananda, who lived probably in the middle of the fifteenth century. He wrote that the Vedanta consists of the Upanishads, the Brahma-Sutras, the Gita, and the commentaries on those texts. The specific reference is in his Vedantasara 3 (The Essence of Vedanta). I will have to do some further research to see if he actually uses the term in question.