The Báb forbade His followers to ask questions of Him Whom God will make manifest (Bahá'u'lláh), unless their questions were submitted in writing and pertained to subjects worthy of His lofty station. See Selections from the Writings of the Báb.
Bahá'u'lláh removes this prohibition of the Báb. He invites the believers to ask such questions as they "need to ask", and He cautions them to refrain from posing "idle questions" of the kind which preoccupied "the men of former times".