Qays bin Abi Hazim said that when the Messenger of Allah (peace and blessings be upon him) passed away, Sayyiduna Bilal (may Allah be pleased with him) said to Sayyiduna Abu Bakr (may Allah be pleased with him): "If you bought me for yourself, then keep me with you; and if you freed me for Allah, then leave me to work for Allah, the Mighty and Majestic."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1006