Musannaf Ibn Abi Shaybah 24327 — A free man who declares himself

It is narrated from al-Harith that a man said: "I was the slave of so-and-so," or "My father was the slave of so-and-so," or "My mother was the slave woman of so-and-so." That so-and-so then said: "You are my slaves today." He said: If they were already free and it is known that they are freedmen (mawali), they will not be counted as slaves merely by a claim, unless upright witnesses are brought who testify that they are his slaves to this day.