The Kitáb-i-Aqdas - The Most Holy Book
Index term: when travelling, under Obligatory Prayer(s)
k14.
When travelling, if ye should stop and rest in some safe spot, perform ye -- men and women alike -- a single prostration in place of each unsaid Obligatory Prayer, and while prostrating say "Glorified be God, the Lord of Might and Majesty, of Grace and Bounty". Whoso is unable to do this, let him say only "Glorified be God"; this shall assuredly suffice him. He is, of a truth, the all-sufficing, the ever-abiding, the forgiving, compassionate God. Upon completing your prostrations, seat yourselves cross-legged -- men and women alike -- and eighteen times repeat "Glorified be God, the Lord of the kingdoms of earth and heaven". Thus doth the Lord make plain the ways of truth and guidance, ways that lead to one way, which is this Straight Path. Render thanks unto God for this most gracious favour; offer praise unto Him for this bounty that hath encompassed the heavens and the earth; extol Him for this mercy that hath pervaded all creation.
n21.
When travelling, if ye should stop and rest in some safe spot, perform ye -- men and women alike -- a single prostration in place of each unsaid Obligatory Prayer
Exemption from obligatory prayer is granted to those who find themselves in such a condition of insecurity that the saying of the Obligatory Prayers is not possible. The exemption applies whether one is travelling or at home, and it provides a means whereby Obligatory Prayers which have remained unsaid on account of these insecure circumstances may be compensated for.
Bahá'u'lláh has made it clear that obligatory prayer "is not suspended during travel" so long as one can find a "safe spot" in which to perform it (Q&A 58).
Numbers 21, 58, 59, 60, and 61 in Questions and Answers amplify this provision.
q21.
 
Question: Concerning the holy verse: "When travelling, if ye should stop and rest in some safe spot, perform ye . . . a single prostration in place of each unsaid Obligatory Prayer . . ."
Answer: This prostration is to compensate for obligatory prayer omitted in the course of travel, and by reason of insecure circumstances. If, at the time of prayer, the traveller should find himself at rest in a secure place, he should perform that prayer. This provision regarding the compensating prostration applieth both at home and on a journey.
q58.
 
Question: Concerning the blessed verse, "When travelling, if ye should stop and rest in some safe spot, perform ye . . . a single prostration in place of each unsaid Obligatory Prayer": is this compensation for the Obligatory Prayer missed by reason of insecure circumstances, or is obligatory prayer completely suspended during travel, and doth the prostration take its place?
Answer: If, when the hour of obligatory prayer arriveth, there be no security, one should, upon arrival in safe surroundings, perform a prostration in place of each Obligatory Prayer that was missed, and after the final prostration, sit cross-legged and read the designated verse. If there be a safe place, obligatory prayer is not suspended during travel.
q59.
 
Question: If, after a traveller hath stopped and rested it is the time for obligatory prayer, should he perform the prayer, or make the prostration in its stead?
Answer: Except in insecure circumstances omission of the Obligatory Prayer is not permissible.