Law of Cause and effect:

" The kind of seed sown
will produce that kind of fruit.
Those who do good will reap good results.
Those who do evil will reap evil results.
If you carefully plant a good seed,
You will joyfully gather good fruit. "
~ Dhammapada


It is mentioned in Dhammapada too, if we do some good things, then good things will come to us. If we do something evil, then evil things will happen to us. It is all due to cause and effect. This law of Cause and effect is known Karma.