بسم الله الرحمن الرحيم
“Every action has an equal and opposite reaction.” thus states Newton’s third law of (natural) motion. Whatever may be your action, there is bound to be a reaction; and nothing that illustrates this theory better than the shari’ idea of recompense. Rather, a good action may return a reward greater than the act itself.
It is authentically attributed to the eminent Companion, Ibn Mas’ood رضي الله عنه that he said, when advising people of causes and consequences:
تعودوا الخير فإنما الخير في العادة
❝ Get in the habit of doing good, for indeed doing good becomes habitual. ❞ [Al-Musannaf ibn Abi Shaybah, 4/165 (#4993)]
In other words, nurturing and priming oneself to enact good deeds will over time, accustom him to regular fulfillment of that deed. And it is revealed:
هَلْ جَزَاءُ الْإِحْسَانِ إِلَّا الْإِحْسَانُ
❝ Is the reward for good (anything) except good? ❞ [Al-Rahman, 60]