There are at least three statements by Nelson Mandela which relate to Johannesburg. The first two, which were discussed before, are his statement in his defense against criminal charges in the Rivonia Trial, April 1964 and his newspaper article about South Africa’s first decade of democracy, April 2004.
On June 1, 2004, Mandela announced his retirement from public life in a speech at the offices of The Nelson Mandela Foundation in Johannesburg. Here are extracts from his speech (verbatim) that day.
Announcement of Retirement 
“I am turning 86 in a few weeks time and that is a longer life than most people are granted. I have the added blessing of being in very good health, at least according to my doctors. I am confident that nobody present here today will accuse me of selfishness if I ask to spend time, while I am still in good health, with my family, my friends and also with myself.”
“One of the things that made me long to be back in prison was that I had so little opportunity for reading, thinking and quiet reflection after my release. I intend, amongst other things, to give myself much more opportunity for such reading and reflection. And of course, there are those memoirs about the presidential years that now really need my urgent attention.”
“I do not intend to hide away totally from the public, but henceforth I want to be in the position of calling you to ask whether I would be welcome, rather than being called upon to do things and participate in events. The appeal therefore is: don’t call me, I’ll call you.”
“This does, however, not mean that the work that we have been involved in, supported and promoted comes to an end. It has been our practice to establish organizations to do certain work and then to leave it to those organization to get on with the job.”
“The leadership of what we call, the three Mandela legacy organizations  are present here today as proof and assurance that our work will continue, perhaps in an even more focused way now that the attention shifts from the individual to the organizations.” 
“We are now able to concentrate very clearly on the work of these three independent but interlinked legacy organizations. I am very satisfied to tell you that they are in full alignment with one another, each charged to giving expression to a specific aspect of human development. The work of the three foundations is distinct but complimentary and supportive of one another.”
“Thank you very much for your attention and thank you for being kind to an old man – allowing him to take a rest, even if many of you may feel that after loafing somewhere on an island [Robben Island] and other places for 27 years the rest is not really deserved.”
 Nelson Mandela Foundation, Retirement Announcement by former President Nelson Mandela (June 1, 2004).
 The Mandela Legacy organizations are The Nelson Mandela Foundation, The Nelson Mandela Children’s Fund and The Mandela Rhodes Foundation. The last of these established a joint venture with The Rhodes Trust to create a Scholarship and Leadership Development program for young leaders from 25 African countries. This blogger was present in July 2003 when Mandela announced this new venture at Westminster Hall in London. (See these posts to dwkcommentaries.com: Celebrating the Rhodes Scholarships’ Centennial (June 21, 2011); Nelson Mandela Makes Connection with Cecil Rhodes (May 20, 2018).)