Saṃyuktāgama 207. [Second Discourse at Jīvaka’s Mango Grove]
Thus have I heard. At one time the Buddha was staying at Vesālī in Jīvaka’s Mango Grove.
At that time the Blessed One said to the monks: “You should cultivate boundless concentration, energetically and with collected mindfulness. Why is that? Having cultivated boundless concentration, energetically and with collected mindfulness, [things] then manifest as they really are. What manifests as it really is? The eye manifests it really is … to be spoken in full up to … All these things, being impermanent and conditioned, manifest as they really are.”
When the Buddha had spoken this discourse, hearing what the Buddha had said the monks were delighted and received it respectfully.