This reminds me of the Edgar A Guest poem my kids recently memorized:

Kindness
by
Edgar Guest

One never knows
How far a word of kindness goes;
One never sees
How far a smile of friendship flees.
Down, through the years,
The deed forgotten reappears.

One kindly word
The souls of many here has stirred.
Man goes his way
And tells with every passing day,
Until life's end:
"Once unto me he played the friend."

We cannot say
What lips are praising us to-day.
We cannot tell
Whose prayers ask God to guard us well.
But kindness lives
Beyond the memory of him who gives.