Bilal said to Abu Bakr, "If you bought me for yourself, then keep me. But if you bought me for the sake of Allah, then leave me to the work of Allah."
إن بلالا قال لأبي بكر: إن كنت إنما اشتريتني لنفسك فأمسكني، وإن كنت إنما اشتريتني لله فدعني وعمل الله.
Bukhari narrated it in Fadail al-Sahabah (3755) from Ibn Numayr, from Muhammad bin Ubayd, who said, Ismail narrated to us, from Qays, and he mentioned it.