This has been called the "milestone" discourse. However, it is believed to be not a real discourse by Sathya Sai Baba but a series of sentences crafted from previous discourses by N. Kasturi. This speech does not appear in the Sathya Sai Speaks series, and no old-timer at Prasanthi NIlaym remembers it.
This article indicates where each sentence came from.
This video was developed by the late Richard Bock in 1968-69. Kasturi reads this "discourse" while we see darshan scenes. The speech also appeared on a long-playing (33RPM) record and appears in Sam Sandweiss's book The Holy Man and The Psychiatrist.
Read the discourse at sathyasai.org/discour/1968/d681123.htm
Audio (Kasturi reciting the "discourse"): mp3 file (22MB) mp3 file (2.2MB)
Here is the actual discourse on 23 November 1968.