The two faithful brothers of Bahá’u’lláh “who accompanied Him on that journey”

Of the two brothers who accompanied Him on that journey the first was Mírzá Músá, commonly called Áqáy-i-Kalím, His staunch and valued supporter, the ablest and most distinguished among His brothers and sisters, and one of the “only two persons who,” according to Bahá’u’lláh’s testimony, “were adequately informed of the origins” of His Faith. The other was Mírzá Muhammad-Qulí, a half-brother, who, in spite of the defection of some of his relatives, remained to the end loyal to the Cause he had espoused. 

- Shoghi Effendi  (‘God Passes By’)

Bahá’u’lláh describes the severity of the journey to Baghdád

…until, finally, Thy [God's] decree was irrevocably fixed, and Thy behest summoned this servant to depart out of Persia, accompanied by a number of frail-bodied men and children of tender age, at this time when the cold is so intense that one cannot even speak, and ice and snow so abundant that it is impossible to move. 

- Baha’u’llah  (Quoted by Shoghi Effendi in ‘God Passes By’)

Comparison of this “enforced and hurried departure of Bahá’u’lláh from His native land” and “the banishment of Abraham from Ur of the Chaldees to the Promised Land”

This enforced and hurried departure of Bahá’u’lláh from His native land, accompanied by some of His relatives, recalls in some of its aspects, the precipitate flight of the Holy Family into Egypt; the sudden migration of Muhammad, soon after His assumption of the prophetic office, from Mecca to Medina; the exodus of Moses, His brother and His followers from the land of their birth, in response to the Divine summons, and above all the banishment of Abraham from Ur of the Chaldees to the Promised Land—a banishment which, in the multitudinous benefits it conferred upon so many divers peoples, faiths and nations, constitutes the nearest historical approach to the incalculable blessings destined to be vouchsafed, in this day, and in future ages, to the whole human race, in direct consequence of the exile suffered by Him Whose Cause is the flower and fruit of all previous Revelations.

‘Abdu’l Bahá, after enumerating in His “Some Answered Questions” the far-reaching consequences of Abraham’s banishment, significantly affirms that “since the exile of Abraham from Ur to Aleppo in Syria produced this result, we must consider what will be the effect of the exile of Bahá’u’lláh in His several removes from Tihrán to Baghdád, from thence to Constantinople, to Rumelia and to the Holy Land.”

- Shoghi Effendi  (‘God Passes By’)