Thanks @Gabriel_L. Seems there’s not much in the early Buddhist texts. I think the Milinda Pañha is considered one of the later of the Khuddaka, Buddhacarita written in classical Sanskrit would also be placed relatively late. The oldest surviving text of sāṁkhya, the SāṁkhyaKārikā, is also dated to a few hundred years CE. Whether you can make the claim that it relied on oral tradition stretching back further, I’m not sure. I haven’t studied that sāṁkhya text in depth or read any studies on it, but from what I have seen it really stresses metaphysical doctrine and doesn’t really make mention of meditation. However, taking the sāṁkhya hint from these later Buddhist texts I’ll armchair theorize…
As I mentioned in this other thread on Patañjala Yoga, it seems that those sutras had a metaphysical basis in samkhya but were preserving a meditative tradition. Maybe we could say that PYS is the best clue we have as to the tradition of the teachers Kālāma and Rāmaputta?
Of course, this meditative yoga tradition would probably be different from the hardcore ascetic yoga we see referenced at other places in the suttas, such as with the dog and cow penance practicing ascetics, or the rude matted-hair ascetics. These more hardcore tapasyins, the kinds that would bake their bodies in the sun (by the way, probably the origin of the ‘tapas’ term which literally means to burn, but later took on the meaning of spiritual heat), the kinds that would stand on one leg nearly all the time, or would raise one arm until it atrophies; these kinds of ascetics have probably existed in India for a very very long time and it is unlikely that they would have many written records (especially if they chose to raise their writing hand! ).
One example I think is rather interesting comes from Punjab, 4th c. BCE, members of Alexander the Great’s company (emph. mine):
fifteen men standing in different postures, sitting or lying down naked, who continued in these positions until the evening, and then returned to the city. The most difficult thing to endure was the heat of the sun, which was so powerful, that no one else could endure without pain to walk on the ground at mid-day with bare feet.’ Two more ascetics called upon the king. ‘They came up to Alexander’s table and took their meal standing, and they gave an example of their fortitude by retiring to a neighbouring spot, where rain, which had now set in, it being the commencement of spring. The other stood on one leg, with a piece of wood three cubits in length raised in both hands; when one leg was fatigued he changed the suppor to the other, and thus continued the whole day.’
The written records for yoga of any kind are sparse in the early period, but there are two disctinct traditions and periods of yogic literature that produced quite a lot of works - the Tantic from ~6th-12th c. CE and the Haṭhic from ~12th-colonial. Both of these later traditions could be seen to contain elements drawn from the two earlier yogic groupings theorized above, haṭha more the inheritor of the ascetic stream.
Anyway, all that we have to rely on is some loose guesswork. I find this kind of comparitive study to be interesting though.