The Iron Ball
Ayoguḷa Sutta  (SN 51:22)

Near Sāvatthī. Then Ven. Ānanda went to the Blessed One and, on arrival, having bowed down to him, sat to one side. As he was sitting there, he said to the Blessed One, “Lord, does the Blessed One have direct experience of going to the Brahmā world by means of supranormal power with a mind-made body?

“Yes, Ānanda, I have direct experience of going to the Brahmā world by means of supranormal power with a mind-made body.”

“But does the Blessed One also have direct experience of going to the Brahmā world by means of supranormal power with this very physical body, composed of the four great elements?”

“Yes, Ānanda, I have direct experience of going to the Brahmā world by means of supranormal power with this very physical body, composed of the four great elements.”

“It’s amazing & astounding that the Blessed One is capable1 of going to the Brahmā world by means of supranormal power with a mind-made body and has direct experience of going to the Brahmā world by means of supranormal power with this very physical body, composed of the four great elements.”

“Tathāgatas are both amazing, Ānanda, and endowed with amazing qualities. They are both astounding and endowed with astounding qualities. Whenever the Tathāgata merges his body with his mind and his mind with his body and remains having alighted on the perception of ease & buoyancy with regard to the body, then his body becomes lighter, more pliant, more malleable, & more radiant.

“Just as when an iron ball heated all day becomes lighter, more pliant, more malleable, & more radiant; in the same way, whenever the Tathāgata merges his body with his mind and his mind with his body and remains having alighted on the perception of ease & buoyancy with regard to the body, then his body becomes lighter, more pliant, more malleable, & more radiant.

“Whenever the Tathāgata merges his body with his mind and his mind with his body, and remains having alighted on the perception of ease & buoyancy with regard to the body, then his body rises effortlessly from the earth up into the sky. He then experiences manifold supranormal powers. Having been one he becomes many; having been many he becomes one. He appears. He vanishes. He goes unimpeded through walls, ramparts, & mountains as if through space. He dives in & out of the earth as if it were water. He walks on water without sinking as if it were dry land. Sitting cross-legged he flies through the air like a winged bird. With his hand he touches & strokes even the sun & moon, so mighty & powerful. He exercises influence with his body even as far as the Brahmā worlds.

“Just as a tuft of cotton seed or a ball of thistle down, lightly wafted by the wind, rises effortlessly from the earth up into the sky, in the same way, whenever the Tathāgata merges his body with his mind and his mind with his body, and remains having alighted on the perception of ease & buoyancy with regard to the body, then his body rises effortlessly from the earth up into the sky. He then experiences manifold supranormal powers. Having been one he becomes many; having been many he becomes one. He appears. He vanishes. He goes unimpeded through walls, ramparts, & mountains as if through space. He dives in & out of the earth as if it were water. He walks on water without sinking as if it were dry land. Sitting cross-legged he flies through the air like a winged bird. With his hand he touches & strokes even the sun & moon, so mighty & powerful. He exercises influence with his body even as far as the Brahmā worlds.”

See also: MN 49