Saṃyuktāgama 126. [Discourse on Being of a Mortal Nature]
Thus have I heard. At one time the Buddha was staying at Mount Makula, at that time being with an attendant monk by the name of Rādha.
Then the Blessed One said to Rādha: “Whatever bodily form, whether past, future or present, internal or external, gross or subtle, sublime or repugnant, far or near, it should all be contemplated as being completely of a mortal nature. Feeling … perception … formations … consciousness is also like this.
The rest should be recited as before.