Mencius. Book 7, Part 2, Chapter 38.
Book 7, Tsin Sin. Part 2.
1. Mencius said, "From Yaou and Shun down to T'ang were five hundred years and more. As to Yun and Kaou-yaou, they saw those earliest sages, and so knew their doctrines, while T'ang heard their doctrines as transmitted, and so knew them.
2. "From T'ang to King Wan were five hundred years and more. As to E Yin and Lae Choo, they saw T'ang and knew his doctrines, while King Wan heard them as transmitted, and so knew them.
3. "From King Wan to Confucius were five hundred years and more. As to T'ae-kung Wang and San E-sang, they saw Wan, and so knew his doctrines, while Confucius heard them as transmitted, and so knew them.
4. "From Confucius downwards until now, there are only one hundred years and somewhat more. The distance in time from the sage is so far from being remote, and so very near at hand was the sage's residence. In these circumstances, is there no one to transmit his doctrines? Yea, is there no one to do so?"
Text source: The Works of Mencius. Translated by James Legge.