Leviticus Rabbah 34:8

Rabbi Yitzchak bar Maryon said, “The Torah teaches a good rule of conduct, that when a person performs a good deed he should do so with a happy heart. If Reuven, for example, had known that the Holy One, blessed be God, would have it written of him, “And Reuven heard it, and delivered [Joseph] out of their hand” (Genesis 37:21), he would have carried Joseph and brought him to his father. And if Aaron had known that the Holy One, blessed be God, would have it written of him “And behold [Aaron] is coming to greet you and he will see you and be happy in his heart” (Exodus 4:14), he would have gone out to greet him with timbrels and dances. And if Boaz had known that the Holy One, blessed be God, would have it written of him that he “Reached her parched corn,” he would have given [Ruth] to eat fatted calves! R. Kohen and R. Joshua son of R. Simon in the name of R. Levi said: In times past when one did a good deed the prophet used to record it, but now if one does a good deed who records it? Elijah and the King Messiah, the Holy One, blessed be God, signing beside them; in accordance with that which is written, “Then they that revered God spoke one with another; and God hearkened, and heard, and a book of remembrance was written before God concerning those who revere God and esteem God’s name” (Malachi 3:16). [AJWS translation]