November 25 or November 26
"In response to your letter of 2 December 1984 asking a question about the event commemorated on the Day of the Covenant, the Universal House of Justice has directed us to send you the following extract from a letter written on behalf of the beloved Guardian on this subject:`The Day of the Covenant Nov. 26th and the Day of the Ascension Nov. 28th, anniversaries of the birth and the Ascension of Abdu'l-Baha must be observed by the friends coming together, but work is not prohibited. In other words the friends must regard observance of these two anniversaries as obligatory - but suspension of work not to be regarded as obligatory.'
"The explanation of how 26 November came to be substituted, in relation to the Birthday of Abdu'l-Baha, for 23 May is related by the late Hand of the Cause Hasan M. Balyuzi in his book, `Abdu'l-Baha', on page 523:`Abdu'l-Baha told the Baha'is that this day was not, under any circumstances, to be celebrated as His day of birth. It was the day of the Declaration of the Bab, exclusively associated with Him. But as the Baha'is begged for a day to be celebrated as His, He gave them November 26th, to be observed as the day of the appointment of the Centre of the Covenant...'
"The House of Justice hopes that this will assist your understanding of the significance of this important date in the Baha'i calendar."
(From a letter written on behalf
of the Universal House of Justice
to the Administrative Committee for South Zaire
January 23, 1984)
(Multiple Authors: Lights of Guidance, Page: 300)