August 18

According to the dear text of the Book of Aqdas and the explicit contents of the Book of the Covenant, ‘Abdu’l-Baha is the Interpreter of all the Works and Books of the Blessed Perfection, and not only of the Book of Aqdas. This question is clear and evident to those who are informed of the Writings and Tablets (of Baha’u’llah). Were this not the case, everyone would have given an interpretation according to his own inclination and considered his interpretation preferable to the interpretation of others - this would naturally lead to great differences. If someone interprets one verse of the Verses of God, and his interpretation is not approved by ‘Abdu’l-Baha, it is not authoritative. 
- ‘Abdu’l-Baha  (From a Tablet, Star of the West, vol. 5, no. 9, August 20, 1914)