In 1787 Newton wrote Thoughts Upon the African Slave Trade to help William Wilberforce's campaign to end the practice—"a business at which my heart now shudders," he wrote. Recollection of that chapter in his life never left him, and in his old age, when it was suggested that the increasingly feeble Newton retire, he replied, "I cannot stop. What? Shall the old African blasphemer stop while he can speak?"