Sri Aurobindo
Letters on Yoga
2. Integral Yoga and Other Paths
The physical Nature does not mean the body alone but the phrase includes the transformation of the whole physical mind, vital, material nature – not by imposing siddhis on them, but by creating a new physical nature which is to be the habitation of the supramental being in a new evolution. I am not aware that this has been done by any Hathayogic or other process. Mental 
or vital occult power can only bring siddhis of the higher plane into the individual life – like the Sannyasi who could take any poison without harm, but he died of a poison after all when he forgot to observe the conditions of the siddhi. The working of the supramental power envisaged is not an influence on the physical giving it abnormal faculties but an entrance and permeation changing it wholly into a supramentalised physical. I did not learn the idea from Veda or Upanishad, and I do not know if there is anything of the kind there. What I received about the supermind was a direct, not a derived knowledge given to me; it was only afterwards that I found certain confirmatory revelations in the Upanishad and Veda.
Current publication:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
Other publications:
Sri Aurobindo. On Himself // SABCL.- Volume 26. (≈ 35 vol. of CWSA) / Popular edition.- Pondicherry: Sri Aurobindo Ashram, 1972.- 514 p.
[Largest or earliest found passage: ] Sri Aurobindo. Letters on Himself and the Ashram // CWSA.- Volume 35. (≈ 26 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2011.- 658 p.
Sri Aurobindo. Letters on Yoga. I // CWSA.- Volume 28. (≈ 22 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2012.- 590 p.
Sri Aurobindo. On Himself and on the Mother // Sri Aurobindo International University Centre Collection.– Volume 1.– First Edition.– Pondicherry: Sri Aurobindo Ashram, 1953.– 782 p.