Step 1: Understanding the Concept:
This question asks to identify the source poem of the given phrase.
Step 2: Detailed Explanation:
This phrase is also from Walt Whitman's "Song of Myself". The full lines are: "Creeds and schools in abeyance, / Retiring back a while sufficed at what they are, but never forgotten, / I harbor for good or bad, I permit to speak at every hazard, / Nature without check with original energy. / I, now thirty-seven years old in perfect health begin, / Hoping to cease not till death." The speaker declares his intention to embark on his poetic project, speaking freely from his experience of nature, and to continue this work for his entire life.
Step 3: Final Answer:
The quote is from Walt Whitman's "Song of Myself". Therefore, option (C) is the correct answer.