Saṃyuktāgama 217. [Second Discourse on the Great Ocean]
Thus have I heard. At one time the Buddha was staying at Sāvatthī in Jeta’s Grove, Anāthapiṇḍika’s Park.
At that time the Blessed One said to the monks: “The so-called ocean is what fools speak about in this world, not what noble ones speak about. The ocean is just more or less water.
“For a person the eye is the great ocean, whose waves are those forms. If one is able to endure the waves of forms, one crosses over the great ocean of the eye and finishes with the waves and whirlpools of its waters, and with its evil reptiles and female demons.
“For a person the ear … the nose … the tongue … the body … the mind is the great ocean, whose waves are … odours … flavours … tangibles … mental objects. If one is able to endure the waves of mental objects, one crosses over the great ocean of the mind and finishes with its waves and whirlpools, and with its evil reptiles and female demons.”
At that time the Buddha spoke a poem:
“The great ocean with its tremendous waves, Its evil reptiles and frightful demons, Is difficult to cross. One who is able to cross it Is free from its waters without remainder.
“Being able to abandon all dukkha, One no more receives a further existence, Forever [has attained] Nirvāṇa, And will never again be negligent.”
When the Buddha had spoken this discourse, hearing what the Buddha had said the monks were delighted and received it respectfully.