It wasn’t just Muslim Arabs, either. Arabs’ involvement in slavery is recorded with reference to Joseph.
Joseph’s brothers sold him either to Ishmaelites or to Midianites—both versions are found in Genesis 37. Supposedly the Yahwist source had Ishmaelites and the Elohist source had Midianites. Ishmael and Midian were both sons of Abraham by different women. I don’t think they are explicitly called Arabs but haven’t made a search.