Leviticus 25:1, 44-46, 55
1 The Lord said to Moses at Mount Sinai, … 44 “‘Your male and female slaves are to come from the nations around you; from them you may buy slaves. 45 You may also buy some of the temporary residents living among you and members of their clans born in your country, and they will become your property. 46 You can bequeath them to your children as inherited property and can make them slaves for life, but you must not rule over your fellow Israelites ruthlessly. 55 … I am the Lord your God.
Not only does the bible not condemn slavery, god actually tells Moses where to get his slaves from. Leviticus chapter 25 lays out some property laws for the Israelites, including buy back clauses, specifically relating to houses in walled and non walled cities, land, and slaves. God tells Moses that if any Israelites become so poor that they have to sell themselves, that they are to be treated as hired workers and are to be released by a certain time. But slaves from other nations are slaves for life. He also says that they must not deal ruthlessly with their fellow Israelites, but gives no such command for the foreign slaves.
Some people try to make the argument that slavery was such an ingrained part of society in the world at that time that it would have been too big of a request for him to try to abolish it all at once. But that argument means that god rated the difficulties the Israelites would have faced by not having slaves, ahead of the other humans being sold as property. And that he would not have been able to sufficiently convince them that slaver as a whole was wrong. Also if god was able to tell the Israelites to mutilate the foreskin on their own penises, disallowing slavery is tame in comparison.