If you Google that quote (and you probably did) you’ll find it all over the place, often with slight variations. These may be variations on how the original could be translated into English. Some of the variations, however, seem to me to be attempts to “improve” earlier English versions.
In the 1978 English translation of the book “Aikido” by Kisshomaru Ueshiba, the quote is:
"Aiki is not a technique to fight with or defeat the enemy. It is the way to reconcile the world and make human beings one family."
In the 1987 book “Abundant Peace” by John Stevens, the quote is:
"Aiki is not an art to fight with or to defeat an enemy. It is a Way in which to harmonize all people into one family."
In the undated “O Sensei Memoirs” by Richard Moon, published sometime after 1994 (www.cityaikido.com/OsenseiMemoirs.pdf)
, the quote is:
"Aikido is not an art to fight with enemies and defeat them. It is a way to lead all human beings to live in harmony with each other like in a big family."
None of these publications states where this quote originated. Perhaps even the authors don’t know. It may have been something O Sensei wrote, something from one of his lectures, or something he said elsewhere. In other words, I doubt that you’ll be able to find the “original” quote in Japanese, as O Sensei said it.
The versions I’ve found all use the word “defeat.” It’s often difficult to translate from one language to another. Perhaps “Aikido is not an art with which to defend
oneself” is a permissible translation to Portuguese.
By the way, why is this so important to you?