Mencius. Book 4, Part 1, Chapter 19.
Book 4, Le Low. Part 1.
1. Mencius said, "Of services which is the greatest? The service of parents is the greatest. Of charges which is the greatest? The charge of one's self is the greatest. That those who do not fail to keep themselves are able to serve their parents is what I have heard. But I have never heard of any, who, having failed to keep themselves, were able notwithstanding to serve their parents.
2. "There are many services, but the service of parents is the root of all others. There are many charges, but the charge of one's self is the root of all others.
3. "The philosopher Tsang, in nourishing Tsang Seih, was always sure to have wine and flesh provided. And when they were being removed, he would ask respectfully to whom he should give what was left. If his father asked whether there was anything left, he was sure to say, 'There is.' After the death of Tsang Seih, when Tsang Yuen came to nourish the philospher Tsang, he was always sure to have wine and flesh provided. But when the things were being removed, he did not ask to whom he should give what was left, and if his father asked whether there was anything left, he would answer 'No'; ‹ intending to bring them in again. This was what is called ‹ 'nourishing the mouth and body.' We may call the philosopher Tsang's practice ‹ 'nourishing the will.'
4. "To serve one's parents as the philospher Ts'ang served his may be accepted as filial piety."
Text source: The Works of Mencius. Translated by James Legge.