In Tandem
Yuganaddha Sutta  (AN 4:170)

On one occasion Ven. Ānanda was staying in Kosambī at Ghosita’s monastery. There he addressed the monks, “Friends!”

“Yes, friend,” the monks responded to him.

Ven. Ānanda said: “Friends, whoever—monk or nun—declares the attainment of arahantship in my presence, they all do it by means of one or another of four paths. Which four?

“There is the case where a monk has developed insight preceded by tranquility. As he develops insight preceded by tranquility, the path is born. He follows that path, develops it, pursues it. As he follows the path, developing it & pursuing it—his fetters are abandoned, his obsessions destroyed.

“Then there is the case where a monk has developed tranquility preceded by insight. As he develops tranquility preceded by insight, the path is born. He follows that path, develops it, pursues it. As he follows the path, developing it & pursuing it—his fetters are abandoned, his obsessions destroyed.

“Then there is the case where a monk has developed tranquility in tandem with insight. As he develops tranquility in tandem with insight, the path is born. He follows that path, develops it, pursues it. As he follows the path, developing it & pursuing it—his fetters are abandoned, his obsessions destroyed.

“Then there is the case where a monk’s mind has its restlessness concerning the Dhamma [Comm: the corruptions of insight] well under control. There comes a time when his mind grows steady inwardly, settles down, and becomes unified & concentrated. In him the path is born. He follows that path, develops it, pursues it. As he follows the path, developing it & pursuing it—his fetters are abandoned, his obsessions destroyed.

“Whoever—monk or nun—declares the attainment of arahantship in my presence, they all do it by means of one or another of these four paths.”

See also: MN 149; SN 35:204; AN 2:29; AN 4:94; AN 10:71