Mencius - Book 3, Part 1, Chapter 2A

When the duke Ting of T'ang died, the prince said to Yen Yû, 'Formerly, Mencius spoke with me in Sung, and in my mind I have never forgotten his words. Now, alas! this great duty to my father devolves upon me; I wish to send you to ask the advice of Mencius, and then to proceed to its various services'

Zan Yû accordingly proceeded to Tsâu, and consulted Mencius. Mencius said, 'Is this not good? In discharging the funeral duties to parents, men indeed feel constrained to do their utmost. The philosopher Tsang said, "When parents are alive, they should be served according to propriety; when they are dead, they should be buried according to propriety; and they should be sacrificed to according to propriety: this may be called filial piety." The ceremonies to be observed by the princes I have not learned, but I have heard these points: that the three years' mourning, the garment of coarse cloth with its lower edge even, and the eating of congee, were equally prescribed by the three dynasties, and binding on all, from the sovereign to the mass of the people.'

Zan Yû reported the execution of his commission, and the prince determined that the three years' mourning should be observed. His aged relatives, and the body of the officers, did not wish that it should be so, and said, 'The former princes of Lû, that kingdom which we honor, have, none of them, observed this practice, neither have any of our own former princes observed it. For you to act contrary to their example is not proper. Moreover, the History says, "In the observances of mourning and sacrifice, ancestors are to be followed," meaning that they received those things from a proper source to hand them down.'
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.