Rantidev was the son of a king named Sankriti. He was very generous and magestic. So much so that he donated and distributed all his wealth among the unfortunates and lived in utter poverty with his family.
Once, he had to go without food and water for a total of 48 days. Due to lack of food his body had started shivering. On the 49th day, he got some food and water from some where. He was about to distribute it among his family members when an ascetic came along and asked for something to eat. It is easy for a millionaire to donate a few hundreds and not even feel a pinch; but the true generosity of a person is manifested when he has to donate that which he dearly wants. True to his nature, Rantidev didn't even flinch before giving some eatables to the ascetic.
After the ascetic left, he again sat down to eat with his family. Just when he'd distributed the food among his family and was about to start his own, a poor man came along. Looking at his pathetic state, Rantidev gave him something to eat. Soon after, another man came along with his dogs saying that he was hungry. So whatever was left from his share of the food, Rantidev gave it to that man and his dogs. Now all he had was some water for one person. That too didn't seem to be destined for him as there came an outcaste. He begged Rantidev for some water. Rantidev felt pity for him and gave him all the water that he had. He proclaimed to God that he wanted to reside in the body of all the people on this earth so that he could absorb the sadness that they experience, leaving them happy; that by offering water to this man all his hunger, thirst and pain had vanished!
This was actually a test by Brahma, Vishnu and Mahesh. they had disguised themselves and appeared as all the hungry guests at the door of Rantidev. They were elated to see the patience and devotion exhibited by him and wanted to grant him a boon. So they appeared before him and told him so. However, Rantidev had done all this without any desire for the fruits of his labor and without any attachment. Hence, he didn't want anything from the Gods. From then on, Rantidev got engrossed in His devotion with all his heart and soul and so did his family.