What is the evidentiary basis for emancipation from the Sunnah?

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The basis in the Sunnah is the narration from Abu Hurayrah, where the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees a believing slave, Allah will free every limb of his corresponding limb from the Fire, until He frees the hand for the hand, the foot for the foot, and the private part for the private part." This tradition is agreed upon (Muttafaq 'alayh), and there are numerous other narrations supporting this.