After some time had passed, Paul said to Barnabas, "Let's go back and visit the brothers in every town where we have preached the message of the Lord, and see how they're doing."
References for Acts 15:36
Barnabas wanted to take along John Mark.
References for Acts 15:37
But Paul did not think it appropriate to take along this man who had deserted them in Pamphylia and had not gone on with them to the work.
There was such a sharp disagreement that they parted company, and Barnabas took Mark with him and sailed off to Cyprus.