Write Injuries in Dust, Benefits in Marble.

Benjamin Franklin (1706–1790) American statesman, scientist, philosopher, aphorist

Poor Richard (1747 ed.)
    (Source)

As with so much else of Franklin's, this phrase is not without earlier forms, e.g.: Thomas More, History of King Richard III (1513):

For men use, if they have an evil turn, to write it in marble; and whosoever does us a good turn, we write it in dust.

Or see Shakespeare, Henry VIII 4.2.45-46 (1613):

Men's evil manners live in brass, their virtues
We write in water.

Variants include "but kindnesses in marble" or "but kindness in marble."

This also shows up as a French saying in various forms:

• "Ecrivez les injures sur le sable, mais les bienfaits sur le marbre."
• "Écrivez les injures sur le sable, gravez les bienfaits sur le marbre."