“God is the best option to put your trust in, instead of relying on another human being, who cannot even keep their own promises to themselves.”

Attributed by William Blacker (not to be confused with Valentine Blacker), who popularized the quote with his poem "Oliver's Advice" http://books.google.com/books?id=JmEaAQAAIAAJ&dq=%22Oliver%27s+Advice%22+Cromwell&q=%22Oliver%27s+Advice%22+Cromwell#v=snippet&q=%22Oliver's%20Advice%22%20Cromwell&f=false, published under the pseudonym Fitz Stewart in The Dublin University Magazine, December 1834, p. 700; where the attribution to Cromwell appears in a footnote describing a "well-authenticated anecdote" that explains the poem's title. The repeated line in Blacker's poem is "Put your trust in God, my boys, but keep your powder dry".
Attributed
Variant: Trust in God and keep your powder dry.
Variant: Put your trust in God, but keep your powder dry.

From the poem "Oliver's Advice" http://books.google.com/books?id=JmEaAQAAIAAJ&dq=%22Oliver%27s+Advice%22+Cromwell&q=%22Oliver%27s+Advice%22+Cromwell#v=snippet&q=%22Oliver's%20Advice%22%20Cromwell&f=false by William Blacker, published under the pseudonym Fitz Stewart in The Dublin University Magazine, December 1834, p. 700. This line by a different Colonel Blacker is paraphrased from an attribution to Oliver Cromwell (hence the poem's title).
Misattributed

The Obedience of A Christian Man (1528)
Context: Where no promise of God is, there can be no faith, nor justifying, nor forgiveness of sins: for it is more than madness to look for any thing of God, save that he hath promised. How far he hath promised, so far is he bound to them that believe; and further not. To have a faith, therefore, or a trust in any thing, where God hath not promised, is plain idolatry, and a worshipping of thine own imagination instead of God. Let us see the pith of a ceremony or two, to judge the rest by. In conjuring of holy water, they pray that whosoever be sprinkled therewith may receive health as well of body as of soul: and likewise in making holy bread, and so forth in the conjurations of other ceremonies. Now we see by daily experience, that half their prayer is unheard. For no man receiveth health of body thereby.
No more, of likelihood, do they of soul. Yea, we see also by experience, that no man receiveth health of soul thereby. For no man by sprinkling himself with holy water, and with eating holy bread, is more merciful than before, or forgiveth wrong, or becometh at one with his enemy, or is more patient, and less covetous, and so forth; which are the sure tokens of the soul-health.

From Freedom in Chains: The Rise of the State and the Demise of the Citizen (St. Martin's Press, 1999) http://www.jimbovard.com/Epigram%20page%20Freedom%20in%20Chains.htm

Source: The Purpose Driven Life: What on Earth Am I Here for?

2001

Source: The Education of a British-Protected Child: Essays

Source: Letter to a Christian Nation