The Upanishads, Part 1 (SBE01), by Max Müller, , at sacred-texts.com
1. What people call sacrifice (yagña), that is really abstinence (brahmakarya). For he who knows, obtains that (world of Brahman, which others obtain by sacrifice), by means of abstinence.
What people call sacrifice (ishta), that is really abstinence, for by abstinence, having searched (ishtvâ), he obtains the Self.
2. What people call sacrifice (sattrâyana), that is really abstinence, for by abstinence he obtains from the Sat (the true), the safety (trâna) of the Self.
What people call the vow of silence (mauna), that is really abstinence, for he who by abstinence has found out the Self, meditates (manute).
3. What people call fasting (anâsakâyana), that is really abstinence, for that Self does not perish (na nasyati), which we find out by abstinence.
What people call a hermit's life (aranyâyana), that is really abstinence. Ara 1 and Nya are two lakes in the world of Brahman, in the third heaven from hence; and there is the lake Airanimadîya, and the Asvattha tree, showering down Soma, and the city of Brahman (Hiranyagarbha) Aparâgitâ 2, and the golden Prabhuvimita (the hall built by Prabhu, Brahman).
Now that world of Brahman belongs to those who find the lakes Ara and Nya in the world of Brahman by means of abstinence; for them there is freedom in all the worlds 3.
131:1 In the Kaush. Br. Up. I, 3, the lake is called Ara, at least according to the commentator.
131:2 In the Kaush. Br. Up. Aparâgita is not pûh, but âyatanam.
131:3 The fifth khanda is chiefly meant to recommend brahmakarya p. 132 or abstinence from all worldly enjoyments, enjoined on the brahmakârin, the student, as a means of obtaining a knowledge of Brahman. But instead of showing that such abstinence is indispensable for a proper concentration of our intellectual faculties, we are told that abstinence is the same as certain sacrifices; and this is shown, not by arguments, but by a number of very far-fetched plays on words. These it is impossible to render in any translation, nay, they hardly deserve being translated. Thus abstinence is said to be identical with sacrifice, yagña, because yo gñâtâ, 'he who knows,' has a certain similarity with yagña. Ishta, another kind of sacrifice, is compared with eshanâ, search; sattrâyana with Sat, the True, the Brahman, and trâyana, protection; mauna, silence, with manana, meditating (which may be right); anâsakâyana, fasting, with nas, to perish, and aranyâgana, a hermit's life, with ara, nya, and ayana, going to the two lakes Ara and Nya, which are believed to exist in the legendary world of Brahman. Nothing can be more absurd. Having once struck the note of Brahmanic legends, such as we find it, for instance, in the Kaushîtaki-brâhmana-upanishad, the author goes on. Besides the lakes Ara and Nya (in the Kaushîtaki-brâhmana-upanishad we have only one lake, called Âra), he mentions the Airammadîya lake, and explains it as aira (irâ annam, tanmaya airo mandas, tena pûrnam airam) and madîya, delightful. The Asvattha tree, which pours down Soma, is not tortured into anything else, except that Soma is explained as the immortal, or nectar. Aparâgita becomes the city of Brahman, because it can be conquered by no one except those who have practised abstinence. And the hall which elsewhere is called Vibhu-pramita becomes Prabhu-vimitam, or Prabhu-vinirmita, made by Prabhu, i.e. Brahman. All the fulfilled desires, as enumerated in khandas 2-5, whether the finding again of our fathers and mothers, or entering the Brahmaloka with its lakes and palaces, must be taken, not as material (sthûla), but as mental only (mânasa). On that account, however, they are by no means considered as false or unreal, as little as dreams are. Dreams are false and unreal, relatively only, i. e. relatively to what we see, when we awake; but not in themselves. Whatever we see in waking, also, has been shown to be p. 133 false; because it consists of forms and names only; yet these forms and names have a true element in them, viz. the Sat. Before we know that Sat, all the objects we see in waking seem true; as dreams seem true in dreaming. But when once we awake from our waking by true knowledge, we see that nothing is true but the Sat. When we imagine we see a serpent, and then discover that it is a rope, the serpent disappears as false, but what was true in it, the rope, remains true.