Musnad Ahmad 30:3670

Yahya ibn Adam narrated to us, Asim—meaning Ibn Muhammad—narrated to us, from Waqid ibn Muhammad, from Sa'id ibn Marjanah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Any Muslim man who emancipates a Muslim man, Allah will save him from the Fire, every limb of his for every limb of his."