It was reported that there were numerous Bábís in Tabríz before the arrival of the Báb

“The success of this energetic man, Mullá Yúsúf-i-Ardibílí, [a Bábí travel teacher] was so great and so swift that, at the very gates of Tauris (Tabríz), the inhabitants of this populous village acknowledged him as their leader and took the name of Bábí’s. Needless to say that, in the town itself, the Bábí’s were quite numerous, even though the government was taking steps to convict the Báb, to punish him and thereby justify itself in the eyes of the people.” 

(Journal Asiatique, 1866, tome 7, pp. 357–358; Footnotes to chapter 12 provided by Shoghi Effendi)

The arrival of the Báb in Tabríz caused a significant stir provoking a warning from the government

The circumstances of His arrival had stirred the people in Tabríz profoundly. A tumultuous concourse of people had gathered to witness His entry into the city.  Some were impelled by curiosity, others were earnestly desirous of ascertaining the veracity of the wild reports that were current about Him, and still others were moved by their faith and devotion to attain His presence and to assure Him of their loyalty. As He walked along the streets, the acclamations of the multitude resounded on every side. The great majority of the people who beheld His face greeted Him with the shout of “Alláh-u-Akbar,” [God is the Most Great] others loudly glorified and cheered Him, a few invoked upon Him the blessings of the Almighty, others were seen to kiss reverently the dust of His footsteps. Such was the clamour which His arrival had raised that a crier was ordered to warn the populace of the danger that awaited those who ventured to seek His presence. “Whosoever shall make any attempt to approach the Siyyid-i-Báb,” went forth the cry, “or seek to meet him, all his possessions shall forthwith be seized and he himself condemned to perpetual imprisonment.” 

- Nabil  (‘The Dawn-Breakers, chapter 12)

The Báb “remained forty days in Tabríz”

According to “A Traveller’s Narrative” (p. 16), the Báb remained forty days in Tabríz. According to Hájí Mu’inu’s-Saltanih’s manuscript (p. 138), the Báb spent the first night, on His arrival in Tabríz, in the home of Muhammad Big. From there He was transferred to a room in the Citadel (the Ark) which adjoined the Masjid-i-‘Alí Sháh. 

Footnotes to chapter 12 provided by Shoghi Effendi)