An animal is not considered unjust and evil because of its cruelty and injustice, for it is not endowed, as is man, with divine qualities; but if man falls into the same evil condition, it is evident that he has permitted the divine qualities with which he was endowed to be overcome by his ungodlike attributes.
(Compilations, Bahá’í Scriptures, p. 406)

As to thy remark, that ‘Abdu’l-Bahá hath said to some of the believers that evil never exists, nay rather, it is a nonexistent thing, this is but truth, inasmuch as the greatest evil is man’s going astray and being veiled from truth.
(Dr. J.E. Esslemont, Bahá’u’lláh and the New Era, p. 195)

But as to evil, there is no doubt that it exerts a very strong influence both in this world and in the next. ‘Abdu’l-Bahá in the “Some Answered Questions” gives us a thorough and true analysis of the problem of evil. You should preferably refer to that book for further explanation on that point.
(Shoghi Effendi, Lights of Guidance, p. 521)

Evil forces do take control of our life, but it is within our power to free ourselves from falling under their subjection. There are, therefore, specific actions that Bahá’ís can take when confronted with [the] kind of situation of which you write, but the principal way in which they can overcome them is to deepen themselves in the Teachings of Bahá’u’lláh so that they will come to recognize the lack of any true reality to such negative forces.
(Universal House of Justice, Lights of Guidance, p. 520)

Evil is non-existent; it is the absence of good; sickness is the loss of health; poverty the lack of riches. When wealth disappears you are poor; you look within the treasure box but find nothing there. Without knowledge there is ignorance; therefore ignorance is simply the lack of knowledge. Death is the absence of life. Therefore on the one hand we have existence; on the other, nonexistence, negation or absence of existence.
(‘Abdu’l-Bahá, Foundations of World Unity, p. 76-79)

Evil to them seems less a terrible than a slavish thing. It is embodied in no mighty Potentate; rather it forms as isolating madness from which higher spirits strive to free the distorted soul.
(Dr. J.E. Esslemont, Bahá’u’lláh and the New Era, p. 208)

In creation there is no evil; all is good. Certain qualities and natures innate in some men and apparently blameworthy are not so in reality. For example, from the beginning of his life you can see in a nursing child the signs of desire, of anger, and of temper. Then, it may be said, good and evil are innate in the reality of man, and this is contrary to the pure goodness of nature and creation. The answer to this is that desire, which is to ask for something more, is a praiseworthy quality provided that it is used suitably. So, if a man has the desire to acquire science and knowledge, or to become compassionate, generous and just, it is most praiseworthy. If he exercises his anger and wrath against the bloodthirsty tyrants who are like ferocious beasts, it is very praiseworthy; but if he does not use these qualities in a right way, they are blameworthy. ... It is the same with all the natural qualities of man, which constitute the capital of life; if they be used and displayed in an unlawful way, they become blameworthy. Therefore it is clear that creation is purely good.
(‘Abdu’l-Bahá, Some Answered Questions, pp. 250- 251)

Indeed the actions of man himself breed a profusion of satanic power. For were men to abide by and observe the divine teachings, every trace of evil would be banished from the face of the earth. However, the widespread differences that exist among mankind and the prevalence of sedition, contention, conflict and the like are the primary factors which provoke the appearance of the satanic spirit. Yet the Holy Spirit hath ever shunned such matters. A world in which naught can be perceived save strife, quarrels and corruption is bound to became the seat of the throne, the very metropolis, of Satan.
(Bahá’u’lláh, Tablets of Bahá’u’lláh Revealed after the Kitáb-i-Aqdas, p. 176-177)

Nevertheless a doubt occurs to the mind—that is, scorpions and serpents are poisonous. Are they good or evil, for they are existing beings? Yes, a scorpion is evil in relation to man; a serpent is evil in relation to man; but in relation to themselves they are not evil, for their poison is their weapon, and by their sting they defend themselves. But as the elements of their poison do not agree with our elements—that is to say, as there is antagonism between these different elements, therefore, this antagonism is evil; but in reality as regards themselves they are good. The epitome of this discourse is that it is possible that one thing in relation to another may be evil, and at the same time within the limits of its proper being it may not be evil. Then it is proved that there is no evil in existence; all that God created He created good. This evil is nothingness; so death is the absence of life. When man no longer receives life, he dies. Darkness is the absence of light: when there is no light, there is darkness. Light is an existing thing, but darkness is nonexistent. Wealth is an existing thing, but poverty is nonexisting. Then it is evident that all evils return to nonexistence. Good exists; evil is nonexistent.
(‘Abdu’l-Bahá, Some Answered Questions, p. 263-264)

Suffering is both a reminder and a guide. It stimulates us better to adapt ourselves to our environmental conditions, and thus leads the way to self improvement. In every suffering one can find a meaning and a wisdom. But it is not always easy to find the secret of that wisdom. It is sometimes only when all our suffering has passed that we become aware of its usefulness. What man considers to be evil turns often to be a cause of infinite blessings. And this is due to his desire to know more than he can. God’s wisdom is, indeed, inscrutable to us all, and it is no use pushing too far trying to discover that which shall always remain a mystery to our mind.
(Shoghi Effendi, Unfolding Destiny, p. 434)

The absence of spiritual qualities, like darkness, has no existence in itself. As the light of spirituality penetrates deep into the hearts, this darkness gradually dissipates and is replaced by virtue.
(From a letter written on behalf of the Universal House of Justice to an individual believer, 23 October, 1994)

The reality underlying this question is that the evil spirit, Satan or whatever is interpreted as evil, refers to the lower nature in man. This baser nature is symbolized in various ways. In man there are two expressions, one is the expression of nature, the other the expression of the spiritual realm. The world of nature is defective. Look at it clearly, casting aside all superstition and imagination. If you should leave a man uneducated and barbarous in the wilds of Africa, would there be any doubt about his remaining ignorant? God has never created an evil spirit; all such ideas and nomenclature are symbols expressing the mere human or earthly nature of man. It is an essential condition of the soil of earth that thorns, weeds and fruitless trees may grow from it. Relatively speaking, this is evil; it is simply the lower state and baser product of nature.
(‘Abdu’l-Bahá, Foundations of World Unity, p. 77)

The source of all evil is for man to turn away from his Lord and set his heart on things ungodly.
(Bahá’u’lláh, Tablets of Bahá’u’lláh, p. 156)

There are no earth-bound souls. When the souls that are not good die they go entirely away from this earth and so cannot influence anyone. They are spiritually dead. Their thoughts can have influence only when they are alive on the earth… But the good souls are given eternal life and sometimes God permits their thoughts to reach the earth to help the people.
(‘Abdu’l-Bahá, Daily Lessons, Received at ‘Akká, 1979 ed., pp. 35-36)

We know absence of light is darkness, but no one would assert darkness was not a fact. It exists even though it is only the absence of something else. So evil exists too, and we cannot close our eyes to it, even though it is a negative existence. We must seek to supplant it by good, and if we see an evil person is not influenceable by us, then we should shun his company for it is unhealthy.
(Shoghi Effendi, Lights of Guidance, p. 512)

We should also remember that most people have no clear concept of the sort of world they wish to build, nor how to go about building it. Even those who are concerned to improve conditions are therefore reduced to combating every apparent evil that takes their attention. Willingness to fight against evils, whether in the form of conditions or embodied in evil men, has thus become for most people the touchstone by which they judge a person’s moral worth. Bahá’ís, on the other hand, know the goal they are working towards and know what they must do, step by step, to attain it. Their whole energy is directed towards the building of the good, a good which has such a positive strength that in the face of it the multitude of evils—which are in essence negative—will fade away and be no more. To enter into the quixotic tournament of demolishing one by one the evils in the world is, to a Bahá’í, a vain waste of time and effort. His whole life is directed towards proclaiming the Message of Bahá’u’lláh, reviving the spiritual life of his fellowmen, uniting them in a divinely created World Order, and then, as the Order grows in strength and influence, he will see the power of that Message transforming the whole human society and progressively solving the problems and removing the injustices which have so long bedevilled the world.
(The Universal House of Justice, Messages 1963 to 1986, p. 284)

… for the soul is prone to evil.
(Bahá’u’lláh, The Summons of the Lord of Hosts, p. 199)

There is no power exercised over the people by those evil souls that have passed away. Good is stronger than evil and even when alive they had very little power. How much less have they after they are dead, and besides they are nowhere near this planet.
(‘Abdu’l-Bahá, Daily Lessons, Received at ‘Akká, 1979 ed., pp. 43-44)