The story of golden mongoose from Mahabharata explains what is true charity in Hinduism.
After winning the great war of Kurukshetra in Mahabharata, Yudhishtira performed a splendid ashwamedha yagna (horse sacrifice) at which he feasted innumerable learned men and women and gave them many valuable gifts.
Proud and happy, he was sitting on his throne with Sri Krishna near him, when he saw a strange sight. The water with which he had washed the feet of the learned men and women had collected into a big pool. Plunging into it repeatedly was an extraordinary mongoose. It was partly golden and partly grey.
People who saw this strange sight wanted to know why the creature was washing itself repeatedly in the pool.
The mongoose said: "Now that you ask me, I shall speak the truth, though it may not please you. Listen, there was a man, named Sakritprastha, a man of great austerities. He was living with his wife and son and the son's wife, eking out his livelihood by collecting the stray seeds of grain lying in the fields after the harvest.
One day he could get only a handful of rice. This was roasted along with the husk and pounded into flour and divided into four shares. After finishing his daily religious rites Sakritprastha sat down to eat.
Just then a tired and famished wayfarer came in and begged for food. The master of the house thereupon offered his share of the food to the guest. But his wife would not allow this, and offered her share instead. Overruling her husband's objection that it was his duty to maintain the household, she insisted that it was the wife's duty to look after her husband. At this stage the son stepped in. He would not allow his old parents to go without food as long as there was his share which could be offered to the guest. But the son's wife said she would not eat while her husband starved! She placed her share at the disposal of the guest.
Thus they disputed among themselves. Ultimately the father washed the guest's feet and gave him his share. Then the wife, the son and the son's wife offered him in turn their shares. The guest was satisfied and the entire family felt that they had not lived in vain.
At that time a golden chariot came down from heaven, with Vishnu's messengers who lifted Sakritprastha and his family and placed them on the chariot. They said: 'Bhagavan Narayana has commanded you to go to Vaikuntha and become His attendants like us.' They then took them to Vaikuntha.
Passing that way at that moment, I happened to brush with my body the water which had been used for washing the guest's feet and which had collected into a tiny pool. Immediately the part of my body which touched the water became golden in colour. Seeing here an immense quantity of water which had been used for washing the feet of learned men I hoped to get the rest of my body also transformed into gold. So I plunged into it. But alas it was of no use!
Having said this, the mongoose disappeared.
Source – From the Malayalam adaptation of the Mahabharata by Thunchathu Ezhuthachan. Translated by M. C. Subramanian in the 1975 edition of The Mountain View.