Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrated: The Prophet (peace and blessings be upon him) said: "Whoever fasts on the day of Arafah, it becomes an expiation for him for (the sins of) two years; and whoever fasts one day of Muharram receives, for each day, the reward of thirty days."
Imam al-Tabarani recorded it in al-Mu'jam al-Saghir. Its chain mentions that al-Haytham bin Habib narrated it from Sallam al-Tawil. The narrator Sallam is da'if (weak). As for al-Haytham bin Habib, I have not seen anyone other than al-Dhahabi speak about him; al-Dhahabi accused him on account of a report that he narrated. Ibn Hibban declared him thiqah (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 5144
Hadith Gradingمحدثین:إسنادہ ضعیف جداً
Hadith Takhrij«اخرجه الطبراني فى المعجم الكبير (11082). اخرجه الطبراني فى المعجم الصغير (963) ، أخرجه المعجم الصغير للطبراني برقم: 924»