Musar על עבודה זרה 6:8

And when he does trust in God, let him not do so because he feels reward is coming to him on account of his good deeds, but he should do all of his deeds for the sake of God, may He be Exalted, who has raised him and carried him in this world and dealt well with him. He must realize that there is not a moment in all the days of his life that the goodness of the Creator is not upon him. And he must consider that, if his good deeds were doubled and multiplied many times over, it would not be one ten-thousandth of what he ought to do because of God's goodness, may He be Blessed, that hovers over him every moment. And after he has thought all this, let him trust in the kindnesses of the Lord, Blessed be He, who is the One who extends kindness and who is more merciful than all the deeds of mercy of man. For God, in His mercy, gives food even to the swarming creatures, from the mighty wild ox to the eggs of lice (Shabbath 107b). And just as God has mercy on these creatures, not because of their good deeds, so will He have mercy on him.