Nagasena Bhiksu Sutra 2.13
T 1670B Nāgasena Bhikṣu Sūtra
Part 2: Dialogues 2.13. Concentration
The king asked Nāgasena, “What is the characteristic mark of concentration?”
Nāgasena replied, “All meritorious deeds have concentration as their chief. All meritorious actions will follow if a person can concentrate his mind.”
Nāgasena gave some similes, “Like the staircase which is supported by a main structure, all meritorious deeds depend on concentration. It is like a king where the whole army, elephants, horses, war chariots and infantry would incline to follow his lead when he goes down to battle with his fourfold army in array. All the Buddha’s teachings and other good qualities follow concentration, it is just as the army follows the king.”
Nāgasena quoted from the Buddhist sutras:
“It is said, ‘Concentration is the foundation of all good qualities. The trainee in the Dharma should first take refuge in concentration. The life of a person is just like the water flowing down the current in constant succession without interruption.’”
“Excellent, Nāgasena.”