From this link:
Om keshavaya svaha
Om narayanaya svaha
Om madhavaya svaha
I have noticed that this achamanam is popular mostly among Telugu speaking communities.
My question: Which scripture is the source for this achamanam?
Âchamana is one of most rituals of Hindu religion and is performed before almost all brahmin rituals in order to gain purity of mind and body.
Here is the explanation of Âchamana in Devibhagwatpurana
Firstly make the ordinary Âchaman three times, and, while inhaling, drink a little of the water of Âchaman, repeating “Om Kes’avâya Svâhâ, Om Nârâyanâya Svâhâ, Om Mâdhavâya Svâhâ.” Then wash your two hands, repeating “Om Gobindâya Namah, Om Visnave Namah.” Then by the root of the thumb rub the lips repeating “Om Madhû sûdanâya Namah, Om Trivikramâya Namah.” So rub the mouth, repeating “Om Vâmamâya Namah, Om S’rîdharâya Namah.” Then sprinkle water on the left hand, saying “Om Hrisîkes’âya Namah.” Sprinkle water on the legs, saying “Om Padmanâbhâya Namah.” Sprinkle water on the head, saying “Om Dâmodarâya Namah.” Touch the mouth with the three fingers of the right hand, saying “Om Samkarsanâya Namah.” Touch the nostrils with the thumb and forefinger saying “Om Vâsudevâya Namah, Om Pradyumnâya Namah.” Touch the eyes with the thumb and ring-finger, saying “Om Aniruddhâya Namah, Om Purusottamâya Namah.” Touch the ears with the thumb and ringfinger saying “Om Adhoksajâya Namah, Om Nârasimhâya Namah.” Touch the navel with the thumb and little finger saying “Om Achyutâya Namah.” Touch the breast with the palm, saying “Om Janârdanâya Namah.” Touch the head saying “Om Upendrâya Namah.” Touch the roots of the two arms saying “Om Haraye Namah, Om Krisnâya Namah.”
While sipping the Âchaman water on the right hand, touch the right hand with your left hand; otherwise; the water does not become pure. While doing Âchaman, make the palm and the fingers all united and close, of the form of a Gokarna (the ear of a cow) and spreading the thumb and the little finger, drink the water of the measure of a pea. If a greater or less quantity be sipped, then that would amount to drinking liquor.