There are three branches of the law. Sacrifice, study, and charity are the first.

-Khandogya Upanishad, 2nd Prapathaka, 23rd Khanda: 1

The eighty verses (of the hymn) are alike food with reference to the gods as well as with reference to man. For all these beings breathe and live by means of food indeed. By food (given in alms, etc.) he conquers this world, by food (given in sacrifice) he conquers the other. Therefore the eighty verses (of the hymn) are alike food, with reference to the gods as well as with reference to man.

- Aitareya-Aranyaka, 2nd Aranyaka, 1st Adhyaya, 2nd Khanda: 13

Let him never turn away ( a stranger) from his house, that is the rule. Therefore a man should by all means acquire much food, for (good) people say (to the stranger): “There is food ready for him.” If he gives food amply, food is given to him amply. If he gives food fairly, food is given to him fairly. If he gives food meanly, food is given to him meanly.

-Taittiriyaka Upanishad, 3rd Valli, 10th Anuvaka: 1