Buddha is said to have given a "silent sermon" once during which he held up a flower and gazed at it. After a while, one of those present, a monk called Mahakasyapa, began to smile. He is said to have been the only one who had understood the sermon. According to legend, that smile (that is to say, realization) was handed down by twenty-eight successive masters and much later became the origin of Zen.
Source: A New Earth: Awakening to Your Life's Purpose, Pages: 2
Contributed by: Tribble