Lecture -- Seattle, October 11, 1968:
Young man (2): What do you think of kuṇḍalinī or rāja-yoga?
Prabhupāda: We are practicing the emperor yoga. Therefore rāja-yoga is included there. The
Bhagavad-gītā says that,
yoginām api sarveṣāṁ
mad-gatenāntarātmanā
śraddhāvān bhajate māṁ yo
sa yuktatamo mataḥ
(BG 6.47)
Anyone who is always thinking of Kṛṣṇa within himself, he is the topmost yogi. Therefore a person who is in Kṛṣṇa consciousness on the authority of Vedic literature, he is supposed to passed all kinds of yogic principles. What is your understanding of kuṇḍalinī yoga? Do you know?
Young man (2): It's very dangerous.
Prabhupāda: So why do you accept such dangerous thing?
Young man (2): No, I just wanted to know what you thought of it.
Prabhupāda: There is no need of... It is not possible to practice that yoga. Yoga practice... That kuṇḍalinī process of yoga is not possible in this age. It is a very difficult process. So we should recommend not to waste your valuable time following something which is not possible to be done by you. That is our recommendation. But if you have got some hobby, that is a different thing. But it will never be successful. It is very difficult to perform. At the present age, as it is recommended and it is followed, practiced, and experienced, this bhakti-yoga is the only possible way for self-realization. It is made very simple: simply chanting Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma... Anyone can do it. Any part of the world can people practice it, of any age, it doesn't matter, either old, young, or child. We have got many children of our devotees, they are also chanting Hare Kṛṣṇa. And many old men like me, they are also chanting Hare Kṛṣṇa. And these young boys and girls, they are also chanting Hare Kṛṣṇa. So it is universal. And all these boys and girls, they are neither Hindus nor Indians, nor they have any knowledge of Sanskrit. But they easily pick up this Hare Kṛṣṇa and chant and getting the result. So this is the easiest, universal method of self-realization in the present age. Any other practice of yoga system will never be successful. It will be simply waste of time.
taken from: https://vaniquotes.org/wiki/What_do_you_think_of_kundalini_or_raja-yoga%3F