‘Abdul Rahman b. Abban used to buy slaves then he would order his servants to clothe them and then to present them before him. He would then say: “You are all free for the sake of Allah as I seek your assistance [i.e. the reward I receive from freeing you for the sake of Allah] when undergoing the anguish of death.”
Related by Mus’ab b. ‘Uthman
Siyar al-A’lam al-Nubula’ (5/10)
(Read on pg 41, Ibn al-Jawzi, Disturber of the Hearts. Dar As-Sunnah Publishers. Birmingham:2012.)