Valmiki Ramayana Ayodhya Kanda Sarga 106 Shloka 15

यः पुत्रः that son, पितुः father's, समतिक्रान्तम् transgressions, साधु as right, मन्यते sets, तत् that son, लोके in the world, अपत्यम् as son, मतम् is considered, अतः for this, अन्यथा contrary happens, विपरीतम् reverse is so.

One who sets right the wrongs done by his father is a true son. Otherwise the son becomes just the opposite. (He is not a son to the father).