Thus saith the LORD; For three transgressions of Israel, and for four, I will not turn away the punishment thereof; because they sold the righteous for silver, and the poor for a pair of shoes; Amos 2:6
To sell the righteous: The innocent are declared guilty for a bribe; and rich men sell into slavery poor honest people whose only crime was that they were in debt to them, sometimes only to the value of a pair of shoes. This sale of the innocent man gives the connection with the story of Joseph, spoken of by the Rabbis as the innocent victim of hatred and slander.
(Hertz, Dr. J.H., The Pentateuch and Haftorahs, 2nd Ed., Soncino Press, London, 1992, pg 152)