Kiddushin 39 - Reward for a Mitzvah is Another Mitzvah

Orlah (prohibition of the first 3 years of a tree's fruit) reads as follows: in Israel, it is forbidden; if in doubt, it is also prohibited. Outside of Israel, one can go to the field where the Orlah tree grows and buy the fruit, provided that one does not see it being picked.

One who performs an extra mitzvah is getting the goodness of performing another mitzvah, and his life is extended to do it. Thus, the reward for a mitzvah is only another mitzvah, except for respect for the parents and sending away the mother bird, for which extended life is promised.

Art: Still Life with Three Birds' Nests  by Vincent van Gogh