PURIFY YOURSELF GRADUALLY
Anupubbena medhavi thoka thokam khane khane
Kammaro rajatass' eva niddhame malam attano.
By degrees, little by little, from time to time, a wise person should remove his own impurities, as a smith removes (the dross of) silver. 
Once, a brahmin saw a group of bhikkhus rearranging their robes as they were preparing to enter the city for almsfood. He noticed that the robes of some of the bhikkhus touched the ground and got wet because of dew on the grass, so he cleared their path of grass. The next day, he found that as the robes of the bhikkhus touched bare ground, the robes got dirty. So, he covered the path with sand. Then again, he observed that the bhikkhus would sweat when the sun was hot and that they got wet when it was raining. So finally, he built a shelter for the bhikkhus at the place where they gathered before entering the city for almsfood.
When the building was finished, he invited the Buddha and the bhikkhus for almsfood. The brahmin explained how he had performed this meritorious deed step by step. The Buddha replied, 'O Brahmin! The wise perform their acts of merits little by little, and gradually and constantly they remove the impurities of the mind.