With accent marks:
Ка́шу ма́слом не испо́ртишь.
You can't spoil the porridge with butter.
From time immemorial, porridge was loved and respected in Russia. It was cooked from wheat, buckwheat, oats, etc. To make it tastier, people added more butter.
This Russian proverb is used to say that something good can not be bad even in large quantities.
Other Russian proverbs
Who is talking about what, and a lousy one about the bath.
A bad example is contagious.
Strike the iron while it's hot.
Without labor, you can not even catch a fish in the pond.
If you like sledding, you should like to carry the sled.
Water wears away a stone.
A fisherman sees a fisherman from afar.
Get your sleigh ready in summer and your (horse-drawn) cart in winter.