From The Autobiography of Martin Luther King, Jr.:

From the age of three I had a white playmate who was about my age. We always felt free to play our childhood games together. He did not live in our community, but was usually around every day; his father owned a store across the street from our home. At the age of six we both entered school – separate schools, of course. I remember how our friendship began to break as soon as we entered school; this was not my desire but his. The climax came when he told me one day that his father had demanded that he would play with me no more. I never will forget what a great shock this was to me. I immediately asked my parents about the motive behind such a statement.

We were at the dinner table when the situation was discussed, and here for the first time I was made aware of the existence of a race problem. I had never been conscious of it before. As my parents discussed some of the tragedies that had resulted from this problem and some of the insults they themselves had confronted on account of it, I was greatly shocked, and from that moment on I was determined to hate every white person. As I grew older and older this feeling continued to grow.

My parents would always tell me that I should not hate the white man, but that it was my duty as a Christian to love him. The question arose in my mind: How could I love a race of people who hated me and who had been responsible for breaking me up with one of my best childhood friends? This was a great question in my mind for a number of years.