Bhagavad Gita Verse 20, Chapter 17

daatavyamiti yaddaanam deeyatenupakaarine |
deshe kaale cha paatre cha taddaanam saattvikam smritam || 20 ||
 
That which is donated knowing that charity is duty, to whom one is not obliged, in the right place and time, to a worthy person, that charity is called saattvic.
 
daatavyam : charity is duty
iti : in this manner
yat : that
daanam : charity
deeyate : is donated
anupakaarine : to one without obligation
deshe : place
kaale : time
cha : and
paatre : person
cha : and
tat : that
daanam : charity
saattvikam : saattvic
smritam : is called
 
So far, Shri Krishna described the three types of food, sacrifice and penance. Food gives us energy to serve the world, to perform sacrifice. Penance enables us to conserve and channel that energy towards sacrifice. Sacrifice results in a result that is received by the recipient of the sacrifice as well as to us, the performers of the sacrifice. Accumulating results beyond what we need to support ourselves and our family can result in greed. To check this greed, we need to perform daanam or charity.
 
Now, even the attitude towards charity can reveal a lot about the texture of our faith. Shri Krishna described the characteristics or conditions of charity performed with a saattvic attitude. Conducting charity out of a sense of duty is the first condition. It should come naturally to us, and not because someone has asked us to do it. Charity should never be treated as a business deal. For instance, if someone has done us a favour, we should not give him something in the guise of charity. Furthermore, we should not donate something expecting something in return.
 
Charity is a sacred act, therefore it has to be performed thoughtfully. Tossing a coin to a beggar on the street may be a noble act, but it does not quality as an act of saattvic charity. It has to be done at the right place and during an auspicious occasion. It also has to be directed towards a worthy person. Shri Shankaraachaarya in his commentary gives the example of the occasion of Sankraanti, the beginning of the month, as an auspicious occasion. He also gives the example of a learned teacher as one who is worthy of receiving a charitable donation.