Khadíjih-Bagum, the wife of the Báb, witnessed the moment the Báb was appointed by God as the Promised One – recalled by Khadíjih-Bagum

The practice of His Holiness [the Báb] was that each day He would return home about an hour after the sunset and commence devotions, the chanting of the names of God, and writing. About three hours into the night He would have the evening meal and would retire about four hours past sunset. In the morning, He would rise one hour before the dawn and, after washing, would perform His ablutions and then proceed to the upper chambers of the House, which had been set aside as His formal guestroom and formed an outer apartment. There, He stood to recite tablets of visitation, prayers, supplications, and to repeat the names of God. When the sun had risen, Fiddih[a servant] would fire up the samovar and prepare the tea in the chamber occupied by His mother. His Holiness would come down to that apartment and have the morning tea. After that, He would proceed to His merchant office to engage in His own business.

However, one night, unlike other nights, He came home at dusk, saying, “Tell Fiddih to prepare whatever we are having for the evening meal sooner than usual. Tonight I have a particular task to attend to.”

About an hour and a half into the night, the dinner was served, and He joined us for this purpose. Afterwards, Fiddih brought water for Him to wash His blessed hands, and, as usual in the evenings, she spread our bedding and retired to her own quarters. His Holiness retired for the night.

It was not long after that I saw Him rise from the bed and leave the room, going to the outer courtyard. At first, I thought He had gone to the lavatory. When considerable time had passed and He did not return, I was seized by apprehension. I rose from my bed and left the apartment. I looked in the lavatory but did not see Him. Checking the street door, I found it locked from within. I looked in the chamber of His mother and did not find Him there either. By then I was deeply bewildered and perplexed. I walked to the western part of the house and looked up towards the upper chamber, situated on the eastern wing of the House and serving as His private quarters, and saw that it was well-lighted. It seemed as if a thousand lamps illumined the room. This added to my surprise, because there were no guests to require so many lamps. Therefore, full of astonishment, I went up the steps to the room. When I entered, I found that the room was so brilliantly lit that it dazzled my eyes, although there was only a single lamp.

The Báb’s sacrifice

O God, my God! Would that a thousand Ishmaels were given Me, this Abraham of Thine, that I might have offered them, each and all, as a loving sacrifice unto Thee. O my Beloved, my heart’s Desire! The sacrifice of this Ahmad whom Thy servant ‘Alí-Muhammad hath offered up on the altar of Thy love can never suffice to quench the flame of longing in His heart. Not until He immolates His own heart at Thy feet, not until His whole body falls a victim to the cruelest tyranny in Thy path, not until His breast is made a target for countless darts for Thy sake, will the tumult of His soul be stilled.

O my God, my only Desire! Grant that the sacrifice of My son, My only son, may be acceptable unto Thee. Grant that it be a prelude to the sacrifice of My own, My entire self, in the path of Thy good pleasure. Endue with Thy grace My life-blood which I yearn to shed in Thy path. Cause it to water and nourish the seed of Thy Faith. Endow it with Thy celestial potency, that this infant seed of God may soon germinate in the hearts of men, that it may thrive and prosper, that it may grow to become a mighty tree, beneath the shadow of which all the peoples and kindreds of the earth may gather. Answer Thou My prayer, O God, and fulfil My most cherished desire. Thou art, verily, the Almighty, the All-Bountiful.  

- The Báb (Quoted by Nabil in ‘The Dawn-Breakers, translated and edited by Shoghi Effendi)

A reference to Ahmad, the Báb’s son, in Qayyúmu’l-Asma

And there is this further reference to Ahmad in the Qayyúmu’l-Asma:

All praise be to God Who bestowed upon the Solace of the Eyes, in His youth, Ahmad. We did verily raise him up unto God . . . O Solace of the Eyes! [1] Be patient in what thy God hath ordained for thee. Verily He doeth whatsoever He willeth. He is the All-Wise in the exercise of His justice. He is thy Lord, the Ancient of Days, and praised be He in whatever He ordereth. 

- The Báb (Provisional translation by Hand of the Cause Hassan Balyuzi; 'The Báb - The Herald of the Day of Days')

[1] The Báb refers to Himself time and again in this Book as ‘Qurratu‘l-‘Ayn‘—the Solace of the Eyes.