kalindyah salile sive
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Narada Muni instructed: My dear boy, in the waters of the Yamuna River, which is known as Kalindi, you should take three baths daily because the water is very auspicious, sacred and clear. After bathing, you should perform the necessary regulative principles for astanga-yoga and then sit down on your asana [sitting place] in a calm and quiet position.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
It appears from this statement that Dhruva Maharaja had already been instructed how to practice the eightfold yoga system, which is known as astanga-yoga. This system is explained in our Bhagavad-gita As It Is, in the chapter entitled “Dhyana-yoga.” It is understood that in astanga-yoga one practices settling the mind and then concentrating it on the form of Lord Visnu, as will be described in the following verses. It is clearly stated here that astanga-yoga is not a bodily gymnastic exercise, but a practice to concentrate the mind on the form of Visnu. Before sitting on his asana, which is also described in Bhagavad-gita, one has to cleanse himself very nicely in clear or sacred water thrice daily. The water of the Yamuna is naturally very clear and pure, and thus if anyone bathes there three times, undoubtedly he will be very greatly purified externally. Narada Muni, therefore, instructed Dhruva Maharaja to go to the bank of the Yamuna and thus become externally purified. This is part of the gradual process of practicing mystic yoga.