弟子入则孝 (dìzǐrùzéxiào): when at home, the disciple is filial

From 《论语·学而》(Analects, Xue'er 1:6): 弟子入则孝，出则悌，谨而信，泛爱众，而亲仁。行有余力，则以学文 (The disciple: at home, be filial; abroad, be respectful to elders; careful and trustworthy; loving all broadly and close to the humane. With any energy left over, then study the texts). Also the opening of 李毓秀《弟子规》(Qing-era primer, 1662-1722), which expands the passage into a complete children's conduct manual.

usage

Inseparable from 出则悌 (abroad, be respectful to elders). 入/出 here = at home / outside home. 则 = then, in that case. Confucius's sequence: family virtue first, public virtue next, study of texts last. The defining line of traditional Chinese moral education.