I have heard that on one occasion the Blessed One was wandering among the Mallans, together with a large community of monks, and came to a brahman village of the Mallans named Thūna. The brahman householders of Thūna heard that “Gotama the Sakyan contemplative, gone forth from the Sakyan clan, is wandering among the Mallans together with a large community of monks, and has arrived at Thūna.” So they filled the well all the way to the brim with grass & chaff, [thinking], “Don’t let these shaven-headed contemplatives draw drinking water.”
Then the Blessed One, going down from the road, went to a certain tree, and on arrival sat down on a seat laid out. Seated, he said to Ven. Ānanda: “Please, Ānanda, fetch me some drinking water from that well.”
When this was said, Ven. Ānanda replied, “Just now, lord, the brahman householders of Thūna filled that well all the way to the brim with grass & chaff, [thinking], ‘Don’t let these shaven-headed contemplatives draw drinking water.’”
A second time, the Blessed One said to Ven. Ānanda: “Please, Ānanda, fetch me some drinking water from that well.”
A second time, Ven. Ānanda replied, “Just now, lord, the brahman householders of Thūna filled that well all the way to the brim with grass & chaff, [thinking], ‘Don’t let these shaven-headed contemplatives draw drinking water.’”
A third time, the Blessed One said to Ven. Ānanda: “Please, Ānanda, fetch me some drinking water from that well.”
Responding, “As you say, lord,” to the Blessed One, Ven. Ānanda–taking a bowl–went to the well. As he was approaching the well, it expelled all the grass & chaff from its mouth and stood filled to the brim–streaming, as it were–with pristine water, undisturbed & clear. The thought occurred to him, “How amazing! How astounding!–the great power & great might of the Tathāgata!–in that, while I was approaching the well, it expelled all the grass & chaff from its mouth and stood filled to the brim–streaming, as it were–with pristine water, undisturbed & clear.”
Taking drinking water in his bowl, he went to the Blessed One and on arrival said, “How amazing, lord! How astounding!–the great power & great might of the Tathāgata!–in that, while I was approaching the well, it expelled all the grass & chaff from its mouth and stood filled to the brim–streaming, as it were–with pristine water, undisturbed & clear. Drink the water, O Blessed One! Drink the water, O One-Well-Gone!”
Then, on realizing the significance of that, the Blessed One on that occasion exclaimed:
What need for a well
if there were waters always?
Having cut craving
by the root,
one would go about searching
for what?
Read this translation of Udāna 7.9 Udapāna Sutta. The Well by Bhikkhu Ṭhanissaro on DhammaTalks.org.