Кинь в окошко крошки, в дверь придет лепешка

See За добро добром и платят (3)

Cf: Cast thy bread upon the waters, for thou shalt find it after many days (Br.). Cast your bread upon the water; it will return to you a hundredfold (Am.). A good deed comes back a thousandfold (Am.). Scatter with one hand, gather with two (Am., Br.)