What was the relationship between Silas and Paul?
When Paul parted from Barnabas, he chose Silas as his companion. In the prison at Philippi, the two of them prayed and sang hymns to God at midnight. Acts 15:40; Acts 16:25
What the Bible says
Acts 15:40
But Paul choosing Silas, departed, being delivered by the brethren to the grace of God.
Acts 16:25
And at midnight, Paul and Silas praying, praised God. And they that were in prison, heard them.
Douay-Rheims Bible (Challoner revision), public domain.