Rashi on Deuteronomy 16:11/רש"י על דברים ט״ז:י״א

1לוי גר יתום ואלמנה THE LEVITE THE STRANGER, THE FATHERLESS, THE WIDOW — these four are Mine, corresponding to four that are yours, viz., בנך ובתך ועבדך ואמתך THY SON, THY DAUGHTER, THY MAN-SERVANT AND THY MAID-SERVANT; if you gladden Mine, I will gladden yours (Midrash Tanchuma, Re'eh 18).