Kitáb-i-Aqdas

To none is it permitted to mutter sacred verses before the public gaze as he walketh in the street or marketplace   ¶108

This is an allusion to the practice of certain clerics and religious leaders of earlier Dispensations who, out of hypocrisy and affectation, and in order to win the praise of their followers, would ostentatiously mutter prayers in public places as a demonstration of their piety. Bahá'u'lláh forbids such behaviour and stresses the importance of humility and genuine devotion to God.