One of Darwin's big supporters and advocates was the Harvard botanist Asa Gray, who often read Darwin's drafts and ideas and gave him criticism and feedback. He was also one of Darwin's contemporaries to encourage him to publish his abstract of the Origin of Species. He believed in the strength of Darwin's theory of natural selection, all while being a devout Christian. He pushed Darwin to question and explore his own belief in God while advocating for Darwin's theory to the general public and academia. Gray always argued for the compatability of evolution and religion until his death. A lot of Darwin's letters to Gray show how the two discussed the issue of religion. Here is an exerpt of one.
"Certainly I agree with you that my views are not at all necessarily atheistical. The lightning kills a man, whether a good one or bad one, owing to the excessively complex action of natural laws,—a child (who may turn out an idiot) is born by action of even more complex laws,—and I can see no reason, why a man, or other animal, may not have been aboriginally produced by other laws; & that all these laws may have been expressly designed by an omniscient Creator, who foresaw every future event & consequence. But the more I think the more bewildered I become; as indeed I have probably shown by this letter."
Link to the letter I quoted: http://www.darwinproject.ac.uk/entry-2814