But we ask for things which the divine wisdom does not desire for us, and there is no answer to our prayer. His wisdom does not sanction what we wish. We pray, “O God! Make me wealthy!” If this prayer were universally answered, human affairs would be at a standstill. There would be none left to work in the streets, none to till the soil, none to build, none to run the trains. Therefore, it is evident that it would not be well for us if all prayers were answered. The affairs of the world would be interfered with, energies crippled and progress hindered. But whatever we ask for which is in accord with divine wisdom, God will answer. Assuredly!
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 246)
Verily, be not grieved if a thing ye asked of Him remaineth unanswered, inasmuch as He hath been commanded by God to observe silence, a silence which is in truth praiseworthy.
(The Báb, Selections from the Writings of the Báb, p. 48)