Paul and Silas first went to Thessalonica during Paul's second journey. (Acts 17)
He taught in the Jewish synagogue for three Sabbath days. Some Jews were persuaded and a large number of God-fearing Greeks and quite a few prominent women believed.
Other Jews were jealous, rounded up some bad characters, formed a mob and started a riot in the city.
Jeson and other believers were dragged before the city leaders. They were forced to post bail
 and let go.
That night, the believers sent
Paul and Silas to Berea.
This letter was from Paul,
 Silas and Timothy.