Rabbi Phinehas the Priest said in reference to Proverbs 11.21, "If you have fulfilled a command, do not seek its reward from God straightaway, lest you not be acquitted of sin, but be regarded as wicked because you have not sought to cause your children to inherit anything. For if Abraham, Isaac, and Jacob had sought the reward of the good deeds which they performed, how could the seed of these righteous men [e.g., Israel] have been delivered?"

(The Misdrashs)