I was 19 when I first heard the Hollies’ song, “He Ain’t Heavy, He’s My Brother.” Wikipedia says the phrase can be traced back as early as 1884. Wiki reports an early use in a publication came from Ralph Waldo Trine: "Do you know that incident in connection with the little Scottish girl? She was trudging along, carrying as best she could a boy younger, but it seemed almost as big as she herself, when one remarked to her how heavy he must be for her to carry, when instantly came the reply: 'He's na heavy. He's mi brither.'"