Deuteronomy 15:18-20 New Revised Standard Version, Anglicised Catholic Edition (NRSVACE)
18 Do not consider it a hardship when you send them out from you free persons, because for six years they have given you services worth the wages of hired labourers; and the Lord your God will bless you in all that you do.
The Firstborn of Livestock
19 Every firstling male born of your herd and flock you shall consecrate to the Lord your God; you shall not do work with your firstling ox nor shear the firstling of your flock. 20 You shall eat it, you together with your household, in the presence of the Lord your God year by year at the place that the Lord will choose.