by Swami Sivananda
Only thinking of water to be the dress of Prana is enjoined in the Prana-Vidya.
Karyakhyanadapurvam III.3.18 (377)
On account of (the rinsing of the mouth with water referred to in the Prana Vidya) being a reiteration of an act (already ordained by the Smriti), what has not been so ordained elsewhere (is here enjoined by the Sruti).
Karyakhyanat: on account of being a statement of an act (already enjoined by the Smriti); Apurvam: which has not been so enjoined elsewhere.
In regard to Prana Upasana, Achamana is ordained only as reiteration of what is stated elsewhere. What is ordained is only meditation on water as covering food. What is enjoined in Prana Vidya Upasana of Chhandogya Upanishad is not the Achamana, as such. Achamana is enjoined by the Smritis and is common to all. What is ordained is Anagnatatchintana i.e., meditating that the food is covered by water.
In the Chhandogya Upanishad (V.2.2) and the Brihadaranyaka (VI.1.14) there is a reference to the rinsing of the mouth with water before and after meal, thinking that thereby that Prana is dressed.
These texts intimate two things, rinsing of the mouth and meditation on the breath as dressed. A doubt arises whether the texts enjoin both these matters or only the rinsing of the mouth, or only the meditation on breath as dressed.
This Sutra states that the act of rinsing the mouth is already ordained on every one by the Smriti and the act of thinking the water as the dress of Prana is alone enjoined by the Sruti. The act of rinsing the mouth is not a new one and therefor requires no Vedic injunction.