(Exodus 21:3) "If alone (i.e., without a wife) he came, alone shall he go out." What is the intent of this? It is written (9) "If his master gives him a woman" (a Canaanite bondswoman). ("If" here is) optional (and not mandatory). You say "optional," but perhaps it is mandatory. It is, therefore, written "If alone he come, alone shall he go out" — It is optional and not mandatory. These are the words of R. Yishmael.