At this point [Adrianople, early March 1866] Baha'u'llah decided to formally declare to Mirza Yahya[His half-brother] as the nominee of the Báb, His claim to be the Author of a new Revelation, 'Him Whom God shall make manifest', as foretold by the Báb. Of course, Mirza Yahya was well aware of Baha'u'llah's declaration in the Garden of Ridvan and the Tablets subsequently revealed by Him. But now the time had come for the Supreme Manifestation of God to formally announce His station to the one who was nominated by the Báb to be the leader of His followers until the advent of 'Him Whom God shall make manifest'.
In order to communicate this message to Mirza Yahya, Baha'u'llah revealed the Suriy-i-Amr (Surih of Command) in His own handwriting and instructed His amanuensis Mirza Aqa Jan to take the Tablet to Mirza Yahya, read it aloud and demand a conclusive reply from him. On being apprised of the contents of the Tablet and the claims of Baha'u'llah, Mirza Yahya indicated that he needed some time during which to meditate on the subject. The following day he sent a message to Baha'u'llah that he himself had become the recipient of divine Revelation and it was incumbent upon all to obey and follow him.
Such a claim maintained by so perfidious a person evolved the wrath of God and brought about the eventual split between Baha'u'llah and Mirza Yahya. It must be remembered that the majority of the believers in Adrianople were faithful to Baha'u'llah and until then had associated freely with Mirza Yahya and a small number of his henchmen; now the situation changed.
Mirza Yahya's response to the Suriy-i-Amr was a clear signal for separation. Baha'u'llah, who was then residing in the house of Amru'llah, changed His residence to the house of Rida Big. This was on 10 March 1866. Only the members of His own family and one servant moved to this house and He allowed no one else to attain His presence. As a result, the community of exiles was cut off from His blessed person and left entirely on its own. This withdrawal, similar to His withdrawal to the mountains of Kurdistan a few years earlier, plunged the community into a grievous state and created severe tests and trials for the believers. On the other hand, it afforded each one of the exiles the opportunity to choose between Baha'u'llah and His unfaithful brother. (Adib Taherzadeh, ‘The Child of the Covenant, p. 121)