January 23

It is incumbent upon these members (of the Universal House of Justice) to gather in a certain place and deliberate upon all problems which have caused difference, questions that are obscure and matters that are not expressly recorded in the Book. Whatsoever they decide has the same effect as the Text itself. Inasmuch as the House of Justice hath power to enact laws that are not expressly recorded in the Book and bear upon daily transactions, so also it hath power to repeal the same. Thus for example, the House of Justice enacteth today a certain law and enforceth it, and a hundred years hence, circumstances having profoundly changed and the conditions having altered, another House of Justice will then have power, according to the exigencies of the time, to alter that law. This it can do because these laws form no part of the divine explicit Text. The House of Justice is both the initiator and the abrogator of its own laws. 
(‘Abdu’l-Baha, ‘The Will and Testament of ‘Abdu’l-Baha’)