“We must be the change we wish to see in the world.”

There is "no reliable documentary evidence for the quotation", according to an article in The New York Times. Brian Morton, "Falser Words Were Never Spoken" http://www.nytimes.com/2011/08/30/opinion/falser-words-were-never-spoken.html?_r=0, New York Times, 2011-08-29. It is not found as a direct Gandhi quotation in the 98-volume authorized Collected Works of Mahatma Gandhi. Misquotes that Bapu is forced to wear http://articles.timesofindia.indiatimes.com/2011-10-03/ahmedabad/30238203_1_bapu-tushar-gandhi-gandhiji
The earliest evidence for quotes of this type comes from the "Love Project", an initiative begun at 1970 at a high school in Brooklyn, New York by teacher Arleen Lorrance. According to the project's website http://www.consciousnesswork.com/love.htm, "Be the change you want to see happen, instead of trying to change anyone else" was one the principles of the Project "received" by Lorrance in 1970 -- but contemporaneous evidence for this has not been found.
A 1972 newspaper article states: "Instead of advocating change in people and things, ... Love Project encourages people to actually be change itself". [San Antonio Express, 1972-09-28, 76, 'Love Project' Marks End of Quest, Ron, Fulkerson, https://www.newspapers.com/clip/12194386/love_project_1972/]
In 1974, Lorrance wrote, in a report on the Project: "One way to start a preventative program is to be the change you want to see happen." ( "The Love Project" https://books.google.com/books?id=NcTimfiMzYUC&pg=PA85&lpg=PA85&dq=arleen+lorrance+love+project+1972&source=bl&ots=X5fggiqrCZ&sig=JoOzC2X1QU1eePkOBoy-60rJ1RE&hl=en&sa=X&ved=0ahUKEwiAwIv-_a_MAhUBW2MKHYBQDFIQ6AEIQDAH#v=onepage&q=%22be%20the%20change%22&f=false, in Kellough (ed.), Developing Priorities and a Style, MSS, 1974).
In 1976, a newspaper report listed "'Be the change you want to see happen, instead of trying to change anyone else" as one of the principles of the Love Project. 'A Ministry Called "The Love Project", St Louis Post Dispatch, 1976-11-15, p. 36
In 1987, a similar quote was attributed to Gandhi in a New Mexico newspaper: "You must be the change you wish to see in the world". Hollis Engley, "A Long List of Varied Accomplishments" https://www.newspapers.com/clip/5211946/a_long_list_of_varied_accomplishments/, The New Mexican, Santa Fe, NM, 1987-01-11, p. D-1
In 1991,"We must be the change we wish to see in the world" is attributed to Gandhi in Stella Cornelius, "Partners in Conflict Resolution", from Barnaby (ed.), Building a More Democratic United Nations (1991) Google Book link https://books.google.com/books?id=rcYYoLsFNmAC&pg=PA70&dq=%22be+the+change%22+%22wish+to+see%22&hl=en&sa=X&ved=0CB0Q6AEwAGoVChMI4ufD3tSLyQIVFFJjCh1muQX6#v=onepage&q=%22be%20the%20change%22%20%22wish%20to%20see%22&f=false
Arun Gandhi, grandson of Mahatma Gandhi, has attributed the quote to his famous grandfather since at least 2000 https://web.archive.org/web/20000823060048/http://www.jca.apc.org/g21/panelists.htm. See also "Arun Gandhi Shares the Mahatma's Message" by Michel W. Potts, in India - West [San Leandro, California] Vol. XXVII, No. 13 (1 February 2002) p. A34, and "Be the change you wish to see: An interview with Arun Gandhi" by Carmella B'Hahn, Reclaiming Children and Youth [Bloomington] Vol. 10, No. 1 (Spring 2001) p. 6.< It is not clear whether Arun claims to have directly witnessed his grandfather saying it, or whether he heard of it second-hand.
Misattributed