Sri Aurobindo
Letters on Yoga
2. Integral Yoga and Other Paths
No, certainly I did not mean that the Vedantin who sees a greater working behind the appearances of the world is living in a different world from this material one – if I had meant that, all that I had written would be without point or sense. I meant a Vedantin who lives in this world with all its suffering and ignorance and ugliness and evil and has had a full measure of these things, betrayal and abandonment by friends, failure of outward objects and desires in life, attack and persecution, accumulated illnesses, constant difficulty, struggles, stumblings in his yoga. It is not that he lives in a different world, but he has a different way of meeting its ordeals, blows and dangers. He takes them as 
the nature of this world and the result of the ego-consciousness in which it lives. He tries therefore to grow into another consciousness in which he feels what is behind the outward appearance, and as he grows into that larger consciousness he begins to feel more and more a working behind which is helping him to grow in the spirit and leading him toward mastery and freedom from ego and ignorance and he sees that all has been used for that purpose. Till he reaches this consciousness with its larger knowledge of things, he has to walk by faith and his faith may sometimes fail him, but it returns and carries him through all the difficulties. Everybody is not bound to accept this faith and this consciousness, but there is something great and true behind it for the spiritual life.
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. Letters on Yoga. II // CWSA.- Volume 29. (≈ 22-24 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2013.- 522 p.
[Largest or earliest found passage: ] Sri Aurobindo. Letters of Sri Aurobindo: In 4 Series.- Forth Series [On Yoga].- Bombay: Sri Aurobindo Sircle, 1951.- 652 p.