Trials and Fierce Battles (Kitab Al-Fitan Wa Al-Malahim)
Dawud :: Book 35 : Hadith 4241
Narrated Abdullah ibn Mas'ud:
The Prophet (peace_be_upon_him) 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.