Abu Dawud Book 30, Hadith Number 4241.

Chapter : Fitan and their predictions.

Narated By Abdullah ibn Mas’ud : The Prophet (PBUH) said: The mill of Islam will go round till the year thirty-five, or thirty-six, or thirty-seven; then if they perish, they will have followed the path of those who perished before them, but if their religion is maintained, it will be maintained for seventy years. I asked: Does it mean seventy years which remain or seventy years which are gone by? He replied: It means (seventy years) that are gone by.

Abu Dawud said: Those who recorded Khirash, the name of a narrator, are wrong. (The correct name is Hirash).