Sarah Bradford wrote two biographies of Tubman, with this being the latter. Because Tubman could not read or write, she tasked Bradford with sharing her story, and is quoted in the text, which was published within her lifetime. This is the closest we have to Tubman's actual words, HOWEVER it has inaccuracies and is responsible for misinformation that was repeated in future works. It also contains uncensored usage of the N-word, depending on the edition you read. Do not take it as strictly fact, but it is an important part of the literary heritage of Tubman, and source of some information in later works.