Muhammad bin Abi Humayd said: I visited Amrah bint Ubaydullah bin Abbas, and she said: I heard my father say: I heard Sayyiduna Ibn Abbas (may Allah be pleased with them both) say: The Messenger of Allah (peace and blessings be upon him) said: "Whichever believer frees a believer, Allah will free him from Hell for every limb of his (in exchange for every limb of the freed one)."
Imam al-Tabarani (may Allah have mercy on him) said: Al-Nadr narrated it in this way from Muhammad bin Abi Humayd, from Amrah bint Ubaydullah bin Abbas, while Abu Amir al-Aqadi differed from him and said: "Ubaydullah bin Abdullah bin Abbas".
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10594