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"There is the case where a monk, having gone to the wilderness, to the shade of a tree, or to an empty building, sits down folding his legs crosswise, holding his body erect, and setting mindfulness to the fore. Always mindful, he breathes in; mindful he breathes out. 

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"[4] In one whose persistence is aroused, a rapture not-of-the-flesh arises. When a rapture not-of-the-flesh arises in one whose persistence is aroused, then rapture as a factor for Awakening becomes aroused. He develops it, and for him it goes to the culmination of its development. 

Source: Excerpted from a discourse between the Buddha and his disciple on the mindfulness of breathing.