Here is a link to several such Lincoln quotes.
As for Herndon's claims, he is the Michael Cohen of that day-- not to be believed.
Again I refer you to Lincoln's own words on the subject.
Among my favorite is:
The young Lincoln may have had deist or unorthodox theist views, but whether he was the scoffer Herndon portrays is much less certain. In an age of revivalism, he may have been skeptical about some of the religious transports and ecstasies that went on at revivals, and Herndon may have interpreted that as a more thoroughgoing atheism.
Later on, Lincoln apparently believed in a biblical God, but wasn't convinced that salvation was available. He had inherited much of Calvinism from his early years, but it didn't "take right." He got the fatalism, but not the hope. Lincoln was an Old Testament believer but had hesitancies when it came to other Christian dogmas. The phrase "theistic rationalism" has come to be applied to the beliefs of his middle years.
Curiously, some have seen young Lincoln as a Universalist, a believer that all will be saved, and there are even comments by contemporaries to that effect, saying that his youthful manuscript existed and proclaimed the doctrine of universal salvation. That doctrine is quite the opposite of Calvinism or the post-Calvinist fatalism that is so closely associated with the mature Lincoln, so even without Herndon's tales the question of Lincoln's religion is a difficult one.
As he grew older, Lincoln drew closer to Christian orthodoxy and to organized Christianity, but I think he always considered himself something of an outsider, a feeling that would have been encouraged by early anxieties about whether he was saved or damned.
There was much continuity between Lincoln's views and those of the Founders - Washington, Adams, and Jefferson - but there will always be some controversy surrounding Lincoln's beliefs.
In any case, showed respect for those who are Christians.