Please read an Excerpt below taken from

"Sikhism and Tantric Yoga"
by Dr. Trilochan Singh (Link to entire book)

"Yogi Bhajan is using the sacred Sikh mantras and the sacred name of Guru Ram Das as a mantle for his Tantric Sex Yoga which will inevitably lead to mental and physical debauchery of those who take his brand of Sikhism contaminated by crazy sex-energizing asanas seriously."

I have learnt the technique of true Yoga from the divine Guru. The True Guru has revealed this technique with the Light of the divine Word. Within my body He has revealed the Light that pervades all the regions of the earth. To this Light within me I bow and salute every moment. The initiation of the Guru are my Yogic rings and I fix my mind steadfastly on the One Absolute God.i,

A. G. Guru Arjan, Gaudi, p 208

If one does the nauli dhauti karma (of cleaning the intestine with a piece of cloth), and becomes adept in eighty-four asanas, and yogic exercises, he cannot attain any peace of mind by these yogic techniques. Let him do such Japa or Tapa through such techniques for years and years and wander about in search of perfection, he will not attain genuine inner peace even for a moment.
A. G. Guru Arjan, Majh, p 98

Let one practice nauli and dhauti and all the elaborate yogic feats associated with it; let one make an offering of incense and light lamps before the Deity. None of these yogic feats and formal acts of worship match with devotional contemplation of the Name of God.
A. G. Guru Arjan, Sarang, p 1229

The Sidha Yogis perform their sadhana (yogic feats)
With all their efforts, symbols and techniques;
With such methods and formal garbs of holiness,
One cannot attain the Yoga of God's Vision.
It is only attained through companionship of the saints,
And the teachings of the true Guru.
The Guru's Wisdom unveils the Light within us.
A. G. Guru Ram Das, Kanada, p 1297

In the Dasm Granth, Guru Gobind Singh says,

The, Yogis do countless asanas, and practice Yoga according to the eight stages of the text; they bend this way and bow that way hoping to know the Divine; they merely blacken their face with the ignorance of true divine Knowledge. Without inwardly worshiping and contemplating God, they go at last empty-handed to the grave.
Guru Gobind Singh, Akal Ustat 252