Rashi on Exodus 12:44/רש"י על שמות י״ב:מ״ד

1ומלתה אתו אז יאכל בו WHEN THOU HAST CIRCUMCISED HIM THEN SHALL HE EAT THEREOF — “he” means his (the slave’s) master; this tells us that the neglect to circumcise his slaves bars him from eating of the Paschal offering. This is the opinion of R. Joshua. Rabbi Eliezer, however, said: the neglect to circumcise his slaves does not bar him from eating of the Paschal offering. The objection was raised: if this be so what means “Then shall he eat thereof”? — The reply was given: “He” means the slave, not the master (the meaning being that the slave, so long as he is uncircumcised may not eat of it) (cf. Mekhilta).