From Nagarjuna's Treatise on the Great Perfection of Wisdom
If one is able to give all that one has one gains thereby an increased amount of merit. This is illustrated by the case of a painter by the name of Kar.na from the city of Pu.skaraavatii in the state of Greater Tokharestan. He had travelled to the east to the state of Tak.sa'silaa where he served as a painter to that court for a period of twelve years. He received payment of thirty double-ounces of gold for his work and took it back with him when he returned to the city of Pu.skaraavatii in his home state. [When he arrived there] he heard the sound of a drum beating to convene a great assembly. He went there and saw an assembly of the Sangha. With a mind of pure faith he asked the karmadana, "How much would be required to provide a day's food for this assembly?"
The karmadana replied, "Thirty double-ounces of gold would be adequate to supply food for one day." He then immediately took the entire thirty double-ounces of gold and entrusted it to the karmadana saying, "Prepare on my behalf a day's food [for this assembly]. I will return here tomorrow." He then went back to his home empty-handed.
His wife asked him, "What did you earn for your twelve years of work?"
He replied, "I earned thirty double-ounces of gold."
She immediately asked, "Where is the thirty double-ounces of gold now?"
He replied, "It has already been planted in the field of merit."
The wife asked, "What field of merit?"
He replied, "I gave it to the assembly of the Sangha."
His wife then had him bound and sent before a judge that his crime could be dealt with and the matter properly adjudicated. The grand judge asked, "On account of what matter [have you brought him here]?"
The wife replied, "My husband has become crazy and deluded. He worked in royal service in a foreign country for twelve years and earned thirty double-ounces of gold. He had no compassionate regard for his wife or child and so gave it all away to other people. Thus I have relied on his being dealt through judicial decree. Hence I moved to have him swiftly bound and brought forth."
The grand judge then asked her husband, "Why did you not share with your wife and child, preferring instead to give it away to others?
He replied, "In previous lives I did not cultivate merit. In the present life I am poor and so have undergone all manner of bitter suffering. Now, in this life I have encountered the field of merit. If I do not plant merit, in later lives I will still be poor and so poverty will follow upon poverty continuously and there will be no time when I am able to escape it. I now wish to immediately relinquish this state of poverty. It is for this reason that I took all of the gold and gave it to the assembly of Sanghans."
The grand judge was an upasaka who maintained a pure faith in the Buddha. When he heard these words he praised them, saying, "This is an extremely difficult thing to do. You applied yourself diligently and underwent suffering in order to obtain such a small material reward and then were able to take it all and give it to the Sangha. You are a good man." He then took off the string of pearls around his neck and then gave it to the poor man along with his horse and the income which he received from the taxes on an entire village. He then declared to him, "At the beginning when you had made the gift to the assembly of the Sangha but that assembly of sanghans had still not partaken of that food it was a case of the seed still not really having been planted. But now a sprout has already come forth from it. The great fruit [of your good deed] will come forth in the next life."
It is for reasons such as this that it is said that one gains the most merit if one is able to give entirely of that which has been hard to come by.