Prachinsala, Satyayajna, Indradyumna, Jana and Budil, the sons of five famous Rishis, were discussing among themselves as to what Brahman truly is. They could not come to a definite conclusion even after a long discussion, and one of them proposed that they should approach the well-known Rishi named Uddalaka, with a view to dissolving the differences among themselves. According to the custom then prevalent, they all approached the Rishi each with a bundle of fuel from the forest. In such hermitages, a fire used to be perpetually kept up as a symbol of life and knowledge and one who desired to be a pupil had to bring fuel to sustain this perpetual fire.
When Uddalaka saw these young men coming, he understood their object and told them that he fully realised the purpose of their visit but that as he himself had not been able to realise the Supreme he would not be able to help them. He, accordingly, directed them to king Ashwapati, the ruler of Kekaya, who, in his opinion, was competent to give them the desired instruction.
The five young men, therefore, went to the palace of king Ashwapati who was then busy with the performance of a sacrifice (Yajna). He was, however, glad to receive them and he asked them to remain as his guests till the sacrifice was over. After it was over, the king wanted to present each of them with valuable presents but they refused to accept anything, saying that they had come to ask for instruction as to the nature of the Supreme Being. Next morning the king asked them how each of them worshipped Brahman. Prachinsala said, “I worship the heaven as Brahman”. Satyayajna said that he worshipped Brahman in the orb of the sun. Indradyumna declared that he worshipped Brahman in the ether. Jana said that he worshipped Brahman in the air, and lastly, Budil declared that he worshipped Brahman in water. Uddalaka Rishi, who had also come with them, said that he worshipped Brahman in the earth. Then king Ashwapati replied. “I do not say that your methods of worship are wrong, for you are all right in regarding earth, water, fire, air, ether and the sun as manifestations of Brahman, but Brahman is not only immanent in all of them but transcends them. The universe is but a form of Brahman.”
Source: Chandogya Upanishad