See the passage for yourself at 1 Timothy 6:1-2:
Slavery in New Testament times was significantly different than it has been in recent centuries, especially as experienced in the US. As a result of this, we have very little comprehension of just what it was like to be a slave in those days. We can’t even imagine what it must have been like.
Slavery in the New Testament had very little to do with nationality, ethnicity or skin color. It was more based upon economic circumstances, or because of war. In fact, it was not a rare occurrence for a person to sell themselves into slavery to improve their situation or pay a debt. Slavery to a good master was often a better place to be than a poor free person.
Slaves made up a significant portion of many of the early churches written to in the New Testament, and Paul addressed slavery in many of his letters, such as 1 Corinthians 7:21-24, Colossians 3:22-25, Ephesians 6:5-8, and Titus 2:9-10. Peter also addressed slavery in 1 Peter 2:18-25.
But why would Paul address slavery in this letter to Timothy? It may be that some problems had arisen among slaves and master, similar to those issues and attitudes among the younger widows, which Paul spends some time discussing.