Dhammapada 2.3.p13

2.3.p13

So kira pubbe rājā hutvā nagaraṃ padakkhiṇaṃ karonto nalāṭato sede muccante parisuddhena sāṭakena nalāṭantaṃ puñchi, sāṭako kiliṭṭho ahosi. So ‘‘imaṃ sarīraṃ nissāya evarūpo parisuddho sāṭako pakatiṃ jahitvā kiliṭṭho jāto, aniccā vata saṅkhārā’’ti aniccasaññaṃ paṭilabhi. Te kāraṇenassa rajoharaṇameva paccayo jāto.

It appears that in a previous state of existence he was a king. Once, while making a ceremonial circuit of the city, with sweat pouring down his forehead, he wiped his forehead with a clean cloth, whereupon the cloth became soiled. Thought he, “By reason of this body of mine a cloth so clean as this has lost its former character and become soiled. ‘Impermanent, indeed, are all existing things!’” Thus did he acquire the concept of Impermanence. In consequence of this, in a later existence, Removal of Impurity became his salvation.