Srimad Bhagavatam Canto 07, Chapter 12, Text 22

SB 7.12.22

cared vane dvadasabdan
 astau va caturo munih
dvav ekam va yatha buddhir
 na vipadyeta krcchratah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Being very thoughtful, a vanaprastha should remain in the forest for twelve years, eight years, four years, two years or at least one year. He should behave in such a way that he will not be disturbed or troubled by too much austerity.
Srimad Bhagavatam Canto 07, Chapter 12, Text 21
Srimad Bhagavatam Canto 07, Chapter 12, Text 23