Whoso layeth claim to a Revelation direct from God, ere the expiration of a full thousand years...

Whoso layeth claim to a Revelation direct from God, ere the expiration of a full thousand years, such a man is assuredly a lying impostor. We pray God that He may graciously assist him to retract and repudiate such claim. Should he repent, God will, no doubt, forgive him. If, however, he persisteth in his error, God will, assuredly, send down one who will deal mercilessly with him. Terrible, indeed, is God in punishing! Whosoever interpreteth this verse otherwise than its obvious meaning is deprived of the Spirit of God and of His mercy which encompasseth all created things. Fear God, and follow not your idle fancies. Nay, rather, follow the bidding of your Lord, the Almighty, the All-Wise. Erelong shall clamorous voices be raised in most lands. Shun them, O My people, and follow not the iniquitous and evil-hearted. This is that of which We gave you forewarning when We were dwelling in ‘Iráq, then later while in the Land of Mystery, and now from this Resplendent Spot. 

http://reference.bahai.org/en/t/b/KA/ka-4.html#gr37


The Dispensation of Bahá’u’lláh will last until the coming of the next Manifestation of God, Whose advent will not take place before at least “a full thousand years” will have elapsed. Bahá’u’lláh cautions against ascribing to “this verse” anything other than its “obvious meaning”, and in one of His Tablets, He specifies that “each year” of this thousand year period consists of “twelve months according to the Qur’án, and of nineteen months of nineteen days each, according to the Bayán”.

The intimation of His Revelation to Bahá’u’lláh in the Síyáh-Chál of Ṭihrán, in October 1852, marks the birth of His Prophetic Mission and hence the commencement of the one thousand years or more that must elapse before the appearance of the next Manifestation of God.

http://reference.bahai.org/en/t/b/KA/ka-79.html