Charity of Karna:

Karna was famous for his charity. He was popularly known as
' Dana Karna '. But there is only one incident in Maha Bharatha
depicting his charity. Karna, knowing full well that he was committing
a suicidal act, gave his natural ear-rings and armour to Indra.
Even in his dying moments karna had broke his two golden teeth and given as daan to a needy old man who dint have money to perform last rites of his dead son.

(a) Once Duryodhana wanted to compete with Karna in charity.
He wanted to attract people by munificent charities. Indra decided to
show the greatness of Karna to Duryodahana. He created heavy rains
continuously for ten days. 'Then Indra, in the disguise of an old
Brahmin, went to Duryodhana and requested ten cartfuls of dry firewood.
Duryodhana pleaded his inability. Then that pseudo-Brahmin
approached Karna and put forth the same request. Karna immediately
demolished his beautiful palace without any hesitation, pulled out the
wooden beams from the roof and gave that Brahmin all the dry firewood
that he wanted. That Brahmin carried those ten cartfuls of dry
firewood passing before the gate of Duryodhana's palace. Duryodhana
was ashamed of the charity of Karna, his own feudatory.

Note: Similarly Krishna showed to Arjuna in similar context showed greatness of Karna's Charitable Nature

(b) Once Krishna wanted to show the charity of Karna to Dharma
Raja. He created a big mountain of gold and asked Dharma Raja to
distribute it quickly among the poor. Dharma Raja began his charity
but he could not complete it even after taking months together. Then
Krishna called for Karna and asked him to give the gold in charity.
Immediately Karna, showing the hill of gold to Krishna, said: " Sri
Krishnarpanamastu " (=I offer the whole thing to Sri Krishna).
Dharma Raja was astonished to note this.