Genesis 39:1
And Joseph was brought down to Egypt; and Potiphar, an officer of Pharaoh, captain of the guard, an Egyptian, bought him of the hands of the Ishmeelites, which had brought him down thither.
Cross-reference
Genesis 37:28 recounts the actual sale of Joseph to the Ishmaelites — the event summarized in this verse.
Genesis 37:36 gives an earlier account of Joseph's sale to Potiphar — with Midianites instead of Ishmaelites.
In Genesis 40:4, Potiphar, who bought Joseph in 39:1, assigns him to serve the imprisoned officials.
In Genesis 41:12, the cupbearer recalls Joseph as the Hebrew servant of Potiphar, who bought him in 39:1.
Genesis 37:25 describes the Ishmaelite caravan Joseph's brothers saw — setting up the sale that leads here.
Genesis 45:4 has Joseph later identifying himself as the brother sold into Egypt — reflecting back on this sale.
Psalm 105:17 poetically summarizes Joseph being sold as a slave — echoing the event here.
Acts 7:9 adds that jealous patriarchs sold Joseph and God was with him — expanding the context of the sale.