Kevala Kumbhaka and Raja Yoga
Once spontaneous breath retention [Kevala Kumbhaka] is mastered there is nothing unattainable to a Yogi. By the practice of Kevala Kumbhaka he can retain prana [life force] as long as he wants. Practice of Kevala Kumbhaka leads to Raja Yoga. Without Hatha Yoga there cannot be Raja Yoga and without Raja Yoga there cannot be Hatha Yoga. Hence, a Yogi must practice both.
~ Goraksha Paddhati
Note : Classic Yoga texts describe four main types of Yoga viz. Mantra, Hatha, Laya and Raja. Kundalini Yoga is an umbrella term that refers to a combination of practices from any of these four types for the sake of awakening the latent Kundalini Shakti [Adhyatma Shakti or spiritual energy].