anicca-saññā
anicca-saññā:'perception of impermanence',is defined in the Girimānanda Sutta (A.X. 60) as meditation on the impermanence of the five groups of existence.
"Though,with a faithful heart,one takes refuge in the Buddha,his Teaching and the Community of Monks; or with a faithful heart observes the rules of morality,or develops a mind full of loving-kindness,far more meritorious it is if one cultivates the perception of impermanence,be it only for a moment" (A.X. 20).
See A. VI,102; A. VII,48; Ud. IV,1; S. XXII,102.