From: Zanmai ō zanmai
Abruptly transcending all realms, to be greatly honored within the quarters of the buddhas and ancestors—this is sitting with legs crossed. Trampling the heads of the followers of alien ways and the legions of Māra, to be the one here within the halls of the buddhas and ancestors—this is sitting with legs crossed. Transcending the extreme of the extremes of the buddhas and ancestors is just this one dharma. Therefore, the buddhas and ancestors engage in it, without any further task.
The Buddha Śākyamuni addressed the great assembly, saying,
When sitting with legs crossed,
Body and mind realizing samādhi,
One’s majesty, the multitudes respect,
Like the sun illumining the world.
Removed, the lethargy clouding the mind,
The body light, without pain or fatigue;
The awareness similarly light and easy,
One sits calmly, like the dragon coiled.
King Māra is startled and fearful
On seeing depicted [one] sitting with legs crossed,
How much more [on seeing] one who realizes the way,
Sitting calmly without stirring.”
Thus, King Māra is startled and frightened to perceive the depiction of [someone] sitting with legs crossed — how much more [someone] actually sitting with legs crossed; the virtue cannot be fully reckoned. This being the case, the merit of our ordinary sitting is measureless.
... Clearly we know that sitting with legs crossed is the king of samādhis samādhi, is realization and entrance. All the samādhis are the attendants of this king samādhi. Sitting with legs crossed is upright body, is upright mind, is upright body and mind, is upright buddha and ancestor, is upright practice and realization, is upright head, is upright vital artery.
Now crossing the legs of the human skin, flesh, bones, and marrow, one crosses the legs of the king of samādhis samādhi. The World Honored One always maintains sitting with legs crossed; and to the disciples he correctly transmits sitting with legs crossed; and to the humans and gods he teaches sitting with legs crossed. The mind seal correctly transmitted by the seven buddhas is this.
The Buddha Śākyamuni, sitting with legs crossed under the bodhi tree, passed fifty small kalpas [eras of time], passed sixty kalpas, passed countless kalpas. Sitting with legs crossed for twenty-one days, sitting cross-legged for one time — this is turning the wheel of the wondrous dharma; this is the buddha’s proselytizing of a lifetime. There is nothing lacking. This is the yellow roll and vermillion roller [that holds all the Sutras and Commentaries]. ...