Mishkat al-Masabih 30 Fine Qualities كتاب المناقب 272

وَعَن جَابر قا ل: كَانَ عُمَرُ يَقُولُ: أَبُو بَكْرٍ سَيِّدُنَا وَأَعْتَقَ سَيِّدَنَا يَعْنِي بِلَالًا. رَوَاهُ البُخَارِيّ

Jabir told that `Umar used to say, “Abu Bakr is our chief, and he manumitted our chief,” meaning Bilal. Bukhari transmitted it.