Sand and stone... Best short inspiring friendship story

Once two friends argued, and one of them
slapped another. This man felt a pain, but
telling nothing and wrote on the sand:
— Today my best friend slapped me.
They continued walking and found an oasis,
in which wellspring decided to swim. The one
who was slapped, started to sink, but his
friend saved him.
When he regained consciousness, wrote on
the stone: "Today my best friend saved my
life."
Another friend, who slapped and saved his
friend’s life, asked him:
- When I hurt you, you wrote on the sand and
now you are writing on the stone. Why?
His friend said:
- When someone hurts us, we should write it
on the sand, so that the wind could erase it.
But when someone does something good for
us, we must engrave it on the stone, so that
the wind could not erase it.