Kauṣītaki Upaniṣad 2.2.11

2.2.11

eṣa dharmo 'yācato bhavati /

Of him who knows this, the secret doctrine (upaniṣad) is: 'One should not beg.' It is as if, having begged of a village and not having received, one were to sit down, saying: 'I would not eat anything given from here!' and then those very ones who formerly refused him invite him, saying: 'Let us give to you!' Such is the virtue of the non-beggar. Charitable people, however, address him, saying: 'Let us give to you!'