Saṃyuktāgama 173. [Second Discourse on Eradicating Impermanent Things]
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: “You should eradicate impermanent things of the past. Having eradicated those things will be for your benefit and welfare, for your peace and happiness for a long time. What are impermanent things of the past? Past bodily form is an impermanent thing, past desire [for it] is an impermanent thing. You should eradicate those things. Having eradicated those things will be for your benefit and welfare, for your peace and happiness for a long time. Feeling … perception … formations … consciousness is also like this.”
When the Buddha had spoken this discourse, hearing what the Buddha had said the monks were delighted and received it respectfully.
In the same way [discourses should be recited] on future … present … past and present … future and present … past and future … past, future, and present [things should be abandoned].