However, you may purchase male or female slaves from among the foreigners who live among you.  You may also purchase the children of such resident foreigners, including those who have been born in your land.  You may treat them as your property, passing them on to your children as a permanent inheritance.  You may treat your slaves like this, but the people of Israel, your relatives, must never be treated this way.  (Leviticus 25:44-46 NLT)

    If you buy a Hebrew slave, he is to serve for only six years.  Set him free in the seventh year, and he will owe you nothing for his freedom.  If he was single when he became your slave and then married afterward, only he will go free in the seventh year.  But if he was married before he became a slave, then his wife will be freed with him.  If his master gave him a wife while he was a slave, and they had sons or daughters, then the man will be free in the seventh year, but his wife and children will still belong to his master.  But the slave may plainly declare, 'I love my master, my wife, and my children.  I would rather not go free.'  If he does this, his master must present him before God.  Then his master must take him to the door and publicly pierce his ear with an awl.  After that, the slave will belong to his master forever.  (Exodus 21:2-6 NLT)

Difference between a Slave and a Servant

The difference between a servant and a slave is that a servant can leave at any time

Exodus 2:12
"If thou buy a Hebrew Servant, six years he shall serve and in the seventh year he shall go out free for nothing"

Gen 16:1) Now Sarai, Abram's wife, did not bear. And she had a female
slave, an Egyptian, and her name was Hagar.

(Gen 16:2) And Sarai said to Abram, Behold now, Jehovah has kept me from
bearing. I pray you, go in to my slave woman. It may be that I may be built
by her. And Abram listened to the voice of Sarai.

(Gen 20:17) And Abraham prayed to God, and God healed Abimelech and his wife
and his slave women, and they gave birth.

(Gen 24:35) And Jehovah has blessed my master greatly, and he has become
great. And He has given him flocks and herds and silver and gold, and male
slaves and slave women, and camels and asses.

(Gen 29:24) And Laban gave Zilpah his slave woman to his daughter Leah for a
handmaid.

(Gen 29:29) And Laban gave Bilhah his slave woman to his daughter Rachel, to
be her handmaid.

(Exo 2:5) And the daughter of Pharaoh came down to bathe at the river. And
her maidens walked along by the riverside. And when she saw the ark among
the reeds, she sent her slave-girl to bring it.

(Lev 19:20) And whoever lies with a woman with semen, and she is a
slave-girl, betrothed to a husband and not at all redeemed, nor freedom
given her, there shall be an inquest. They shall not be put to death,
because she was not free.

(Lev 25:6) And the sabbath of the land shall be food for you, for you and
for your servant, and for your slave woman and for your hired servant, and
for your stranger who stays with you,

(Lev 25:44) Both your male slaves, and your female slaves whom you shall
have, shall be of the nations that are all around you. You shall buy male
slaves and female slaves from them.

(Deu 15:17) then you shall take an awl and put it through his ear to the
door, and he shall be your servant forever. And also to your slave-girl you
shall do so.

(Deu 16:11) And you shall rejoice before Jehovah your God, you, and your
son, and your daughter, and your male servant, and your slave girl, and the
Levite inside your gates, and the stranger, and the fatherless, and the
widow, those among you, in the place which Jehovah your God has chosen to
place His name there.

(Jdg 19:19) Yet here is both straw and food for our asses. And there is
bread and wine also for me, and for your slave woman, and for the young man
who is with your servants. There is no lack of anything.

(1Sa 8:16) And he will take your male slaves and your slave girls, and your
finest young men, and your asses, and put them to his work.

(Job 19:15) Those who dwell in my house, and my slave-girls, count me as a
stranger; I am a foreigner in their sight.

(Job 31:13) If I despised the cause of my man servant or of my slave-girl,
when they argued with me;

(Joh 8:35) And the slave does not abide in the house forever, but the Son
abides forever.

(Act 2:18) And in those days I will pour out My Spirit upon My slaves and My
slave women, and they shall prophesy.

(Gal 4:22) For it is written: Abraham had two sons, the one out of the
slave-woman, and one out of the free woman.

(Gal 4:23) But, indeed, he out of the slave-woman has been born according to
flesh, and he out of the free woman through the promise;

(Gal 4:30) But what does the Scripture say? "Cast out the slave-woman and
her son; for in no way shall the son of the slave-woman inherit with the son
of the free woman."

(Eph 6:5) Slaves, obey your masters according to the flesh, with fear and
trembling, in singleness of your heart, as to Christ;

(Col 3:22) Slaves, obey your masters according to the flesh in all things;
not with eye-service, as men-pleasers, but in singleness of heart, fearing
God.

(Col 4:1) Masters, give to your slaves what is just and equal, knowing that
you also have a Master in Heaven.

(1Ti 6:1) Let as many slaves as are under the yoke count their own masters
worthy of all honor, so that the name and doctrine of God may not be
blasphemed.

(Tit 2:9) Slaves are to be obedient to their masters, to please them well in
all things, not talking against,