Chapter: The sin of a person who sells a free man
Narrated Abu Huraira:
The Prophet (ﷺ) said, "Allah says, 'I will be against three persons on the Day of Resurrection: -1. One who makes a covenant in My Name, but he proves treacherous. -2. One who sells a free person (as a slave) and eats the price, -3. And one who employs a laborer and gets the full work done by him but does not pay him his wages.' " - Sahih:Al Bukhari:2227 (islam)

-Is there a fatwah from azarh about slavery (check google with حكم الاسترقاق في الاسلام الأزهر)?
- What is a free person, is a polytheist a free person, Is an idolater a free person in Islam?
- Can you just buy a slave at the market from a non-Muslim?