John 16:18

They alone ask leave of thee who believe not in Allah and the Last Day, and whose hearts feel doubt, so in their doubt they waver.

He obtaineth knowledge, who hath faith and is intent on it and who hath his senses under control; obtaining knowledge one findeth the highest tranquillity in no length of time. One who hath no knowledge and no faith, and whose minds is full of doubt, is lost. Neither this world, nor the next, nor happiness, is for him whose mind is full of doubt. Actions do not fetter him, O Dhananjaya, who hath cast off action by devotion, whose doubts have been dispelled by knowledge, and who is self-restrained. Therefore, destroying, by the sword of knowledge, this doubt of thine that is born of ignorance and that dwelleth in thy mind, betake to devotion, (and) arise, O son of Bharata.’”

In sight of Brahma all these offerings Are spread and are accepted! Comprehend That all proceed by act; for knowing this, Thou shalt be quit of doubt. The sacrifice Which Knowledge pays is better than great gifts Offered by wealth, since gifts' worth--O my Prince! Lies in the mind which gives, the will that serves: And these are gained by reverence, by strong search, By humble heed of those who see the Truth And teach it. Knowing Truth, thy heart no more Will ache with error, for the Truth shall show All things subdued to thee, as thou to Me. Moreover, Son of Pandu! wert thou worst Of all wrong-doers, this fair ship of Truth Should bear thee safe and dry across the sea Of thy transgressions. As the kindled flame Feeds on the fuel till it sinks to ash, So unto ash, Arjuna! unto nought The flame of Knowledge wastes works' dross away! There is no purifier like thereto In all this world, and he who seeketh it Shall find it--being grown perfect--in himself. Believing, he receives it when the soul Masters itself, and cleaves to Truth, and comes-- Possessing knowledge--to the higher peace, The uttermost repose. But those untaught, And those without full faith, and those who fear Are shent; no peace is here or other where, No hope, nor happiness for whoso doubts. He that, being self-contained, hath vanquished doubt, Disparting self from service, soul from works, Enlightened and emancipate, my Prince! Works fetter him no more! Cut then atwain With sword of wisdom, Son of Bharata! This doubt that binds thy heart-beats! cleave the bond Born of thy ignorance! Be bold and wise! Give thyself to the field with me! Arise!

Sugriva spoke and sadly sighed: And Lakshman with a laugh replied: "What show of power, what proof and test May still the doubts that fill thy breast?"