There are three branches of the law. Sacrifice, study, and charity are the first. – Chandogy Upanishad, 2nd Prapataka, 23rd Khanda:1.
Let him never turn away (a stranger) from his house, that is the rule. Therefore a man should by all means acquire much food… 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. – Taittirīyaka Upaniṣhad, 3rd Vallī, 10th Anuvāka: 1