What is the exact wording and original source for Ralph Waldo Emerson’s quote about the woods (for example “In the woods we return to reason and faith” or “In the woods is perpetual youth”)?

There isn’t one single, uniformly “exact” wording because Emerson’s famous passage about the woods has been circulated in several close variants. For example, one frequently cited version is:

'In the woods, we return to reason and faith. There I feel that nothing can befall me in life,—no disgrace, no calamity, (leaving me my eyes,) which nature cannot repair.'
  – Ralph Waldo Emerson^[1]

Another common variant expands the idea further. In this version the passage reads:

'In the woods too, a man casts off his years, as the snake his slough, and at what period soever of life, is always a child. In the woods, is perpetual youth.'
  – Ralph Waldo Emerson, from collections such as Nature and Selected Essays^[4][13]

Yet another trimmed version is sometimes seen as:

'In the woods is perpetual youth. In the woods we return to faith and reason.'
  – attributed to Emerson, found in similar Goodreads listings^[2]

Because these variants are all drawn from Emerson’s writings on nature (for instance from his essay “Nature” and later collections such as Nature and Selected Essays), it is hard to pin down a single “original” wording. The differences likely reflect the way his prose has been excerpted and republished over time.