Joel 2:29

And also upon the servants -God tells beforehand that he would be no respecter of persons. He had said, that He would endow every age and sex. He adds here, and every condition, even that of slaves, both male and female. He does not add here, that they shall prophesy. Under the law, God had provided for slaves, that, even if aliens, they should by circumcision be enrolled in His family and people; that they should have the rest and the devotion of the sabbath; and share the joy of their great festivals, going up with their masters and mistresses to the place which God appointed.