Your good deed for the day
Definition 1 of 1
Pro Tip 1/3Context Matters
Use it when the good deed is fresh and just completed, implying it's part of daily moral behavior. 
You returned her lost wallet? That's your good deed for the day!
Pro Tip 2/3Slightly Informal
The phrase has a friendly tone, suitable for casual conversation rather than formal communication. 
Buying lunch for a homeless person? That'll be your good deed for the day.
Pro Tip 3/3Praise or Prompt
Can be used to praise someone's action or to suggest they've met a moral quota. 
Thanks for helping me study, you've done your good deed for the day!