Question:
 also said: "Whoever fasts one day in the sacred month Allah will grant him the reward of thirty days for every day."  Is this Hadeeth authentic?
  also said: "Whoever fasts one day in the sacred month Allah will grant him the reward of thirty days for every day."  Is this Hadeeth authentic?   said:"Whoever fasts one day during the month of Muharram will get a reward of fasting 30 days." This is a fabricated narration as Shaykh Al-Albaani, may Allah have mercy on him, classified it in the As-Silssila Ath-Tha'eefah, Hadeeth number: 413. However, what is confirmed regarding the excellence of fasting during the month of Muharram is what is reported by Imaam Muslim
  said:"Whoever fasts one day during the month of Muharram will get a reward of fasting 30 days." This is a fabricated narration as Shaykh Al-Albaani, may Allah have mercy on him, classified it in the As-Silssila Ath-Tha'eefah, Hadeeth number: 413. However, what is confirmed regarding the excellence of fasting during the month of Muharram is what is reported by Imaam Muslim  that the Prophet
  that the Prophet  said: "The best fasting after the month of Ramadan is during the month of Muharram, and the best prayer after the obligatory prayer is the optional night prayer." There are other narrations that encourage fasting during all the sacred months(i.e. Rajab, Thul-Qi'dah, Thul-Hijjah, Muharram).
  said: "The best fasting after the month of Ramadan is during the month of Muharram, and the best prayer after the obligatory prayer is the optional night prayer." There are other narrations that encourage fasting during all the sacred months(i.e. Rajab, Thul-Qi'dah, Thul-Hijjah, Muharram).Allah Knows best.