That should not be done to others which is against the interest of one's self. This is virtue, put tersely; there are other sorts of virtue, but it is not compulsory that they (the better) should be acted up to.
न तत् परस्य संदध्यात् प्रतिकूलं यदात्मनः। संग्रहेणैष धर्मः स्यात् कामादन्यः प्रवर्तते॥