Guru Nanak on Yoga

Translation of the shabad "Galin Jog Na Hoyee"
Sung by Bhai Harjinder Singh:

Yoga is not in the patched coat,
Yoga is not in the walking stick.
Yoga is not in smearing the body with ashes.

Yoga is not in the earrings,
and not the shaven head.
Yoga is not the blowing of the horn.

By mere words,
Yoga is not attained.

Yoga is not in wandering
to the tombs of the dead;
Yoga is not in sitting in trances.

Yoga is not in wandering
through foreign lands;
Yoga is not in bathing
at sacred shrines of pilgrimage.

Meeting with the True Guru,
doubt is dispelled,
and the wandering mind
is restrained.

Nectar rains down,
celestial music resounds,
and deep within,
wisdom is obtained.

When the horn is blown
without being blown,
then you shall attain
the state of fearless dignity.

One who looks upon all with the same view,
and knows them to be one and the same
he alone is known as a Yogi.

Remaining dead while yet alive -

practice such a Yoga O Nanak!
Remaining unblemished in the midst of the filth 
of the world - this is the way to attain Yoga

Also read Guru Gobind Singh on Yoga: