“The man who abides in the will of God wills nothing else than what God is, and what He wills.”

This attribution occurs in chapter 13 (Ioan. Graphei, 1532, p. 494) http://books.google.com/books?id=rs47AAAAcAAJ&pg=PA494 of the Christian church father's Lactantius's De Ira Dei (c. 318):
"God," he [Epicurus] says, "either wants to eliminate bad things and cannot,
or can but does not want to,
or neither wishes to nor can,
or both wants to and can.
If he wants to and cannot, then he is weak and this does not apply to god.
If he can but does not want to, then he is spiteful which is equally foreign to god’'s nature.
If he neither wants to nor can, he is both weak and spiteful, and so not a god.
If he wants to and can, which is the only thing fitting for a god, where then do bad things come from? Or why does he not eliminate them?"
Lactantius, On the Anger of God, 13.19
Charles Bray, in his 1863 The Philosophy of Necessity: Or, Natural Law as Applicable to Moral, Mental, and Social Science quotes Epicurus without citation as saying a variant of the above statement (p. 41) http://books.google.com/books?id=BebVAAAAMAAJ&pg=PA41 (with "is not omnipotent" for "is impotent"). This quote appeared in "On the proofs of the existence of God: a lecture and answer questions" http://www.atheism.ru/old/KryAth2.html (1960) by professor Kryvelev I.A. (Крывелёв И.А. О доказательствах бытия божия: лекция и ответы на вопросы. М., 1960). And N. A. Nicholson, in his 1864 Philosophical Papers (p. 40), attributes "the famous questions" to Epicurus, using the wording used earlier by Hume (with "is he" for "he is") http://books.google.com/books?id=ZMsGAAAAcAAJ&pg=PA40. Hume's statement occurs in Book X (p. 186) http://books.google.com/books?id=E7dbAAAAQAAJ&pg=PA186 of his renowned Dialogues Concerning Natural Religion, published posthumously in 1779. The character Philo precedes the statement with "Epicurus's old questions are yet unanswered.…". Hume is following the enormously influential Dictionnaire Historique et Critique (1697–1702) of Pierre Bayle, which quotes Lactantius attributing the questions to Epicurus (Desoer, 1820, p. 479) http://books.google.com/books?id=QwwZAAAAYAAJ&pg=PA479.
There has also arisen a further disputed extension, for which there has been found no published source prior to The Heretic's Handbook of Quotations: Cutting Comments on Burning Issues (1992) by Charles Bufe, p. 186: "Is he neither able nor willing? Then why call him God?"
Disputed

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 269.

Poem "O Infante", verse 1.
Message
Original: Deus quer, o homem sonha, a obra nasce.

Source: What On Earth Is About To Happen… For Heaven’s Sake? (2013), p. 223

Source: On the Mystical Body of Christ, p. 414
Context: What is the Church? She is the body of Christ. Join to it the Head, and you have one man: The Head and the body make up one man. Who is the head? He who was born of the Virgin Mary. … And what is His body? It is His Spouse, that is, the Church.... The Father willed that these two, the God Christ and the Church, should be one man. All men are one man in Christ, and the unity of the Christians constitutes but one man. And this man is all men, all men are this man; for all are one, since Christ is one.

Letter (Spring 1850).
Memoirs of Margaret Fuller Ossoli (1852)
Context: I feel perfectly willing to stay my threescore years and ten, if it be thought I need so much tuition from this planet; but it seems to me that my future upon earth will soon close. It may be terribly trying, but it will not be so very long, now. God will transplant the root, if he wills to rear it into fruit-bearing.

"Endeavor" in Godey's Magazine, Vol. 72 (1866), p. 370.
Context: "What is the harvest of thy saints,
O God! who dost abide?
Where grow the garlands of thy chiefs
In blood and sorrow dyed?
What have thy servants for their pains?"
"This only — to have tried."

Too Busy Not to Pray (2008, InterVarsity Press)