Fortunately, you can find many outstanding resources on the topic you have chosen.  Your question was not entirely clear about which type of text you were searching for (nonfiction, fiction, biography, autobiography), so I will give you several resources as a starting point:

1.  Narrative of the Life of Frederick Douglass, an American Slave, Written by Himself by Frederick Douglass.  I would start with this autobiography.  Frederick Douglass escaped slavery and eventually became one of the most powerful voices of the abolition movement in the North.  One of the added bonuses of using this text is that eNotes has both the e-text and numerous supporting pages of analysis and summary. 

2.  Uncle Tom's Cabin by Harriet Beecher Stowe is fiction and tells the story of three slaves and their struggles and hardships.  Her novel became one of the most popular books at the time, with many people coming to sympathize with the unjust treatment of slaves.  Uncle Tom's Cabin quickly became the most widely read pro-abolition text in the U.S. ENotes has the entire e-text of the novel and many additional pages of historical context, summary, and analysis.

3.  Narrative of Sojourner Truth by Sojourner Truth. Like the other three, eNotes also provides the e-text of the entire biography as well as a very informative biography of Sojourner Truth.  A former slave, Sojourner spoke boldly against the evils of slavery and also advocated rights for women.  Another great text to look at would be Sojourner Truth's famous speech "Ain't I a Woman?".

If you want nonfiction, then I highly recommend that you pair Frederick Douglass' autobiography with Sojourner Truth's biography.  ENotes has many resources to aid you in your research, and the breadth and scope of both works will give you ample material on abolition and American slavery.