Rashi on Deuteronomy 15:17/רש"י על דברים ט״ו:י״ז

1עבד עולם [AND HE SHALL BE THY] SERVANT עולם — One might think that עולם has here its usual meaning: for ever! Scripture, however, states, (Leviticus 25:10) “[And ye shall sanctify the fiftieth year and proclaim liberty throughout all the land unto all the inhabitants thereof] and ye shall return every man unto his family”. Consequently, you learn that it (what Scripture terms here עולם), can only mean the period until the termination of that Jubilee cycle (Mekhilta; cf. Rashi on that verse),

2ואף לאמתך תעשה כן AND ALSO UNTO THY MAID SERVANT THOU SHALT DO LIKEWISE — i.e. furnish her out of thy property. One might think, however, that Scripture puts her on the same level with the man-servant concerning the piercing of the ear too! It however, states, (Exodus 21:5) “And if the man-servant (העבד) shall plainly say, [I love my lord … then … his lord shall bore his ear through with an awl]” — so you see that a man-servant must have his ear pierced, but a maid-servant does not have it pierced (Sifrei Devarim 122:6).