“This is a very close paraphrase of a quotation attributed to Carl Buehner in a book published many years earlier - "They may forget what you said - but they will never forget how you made them feel." quoted in Richard Evans' Quote Book, 1971, Publisher's Press, ASIN: B000TV5WBW, although it is widely (mis)attributed to Angelou in her book Worth Repeating: More Than 5,000 Classic and Contemporary Quotes (2003) by Bob Kelly, p. 263,”

Source: Wikiquote