Srimad Bhagavatam Canto 09, Chapter 11, Text 18

SB 9.11.18

tata urdhvam brahmacaryam
 dharyann ajuhot prabhuh
trayodasabda-sahasram
 agnihotram akhanditam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
After mother Sita entered the earth, Lord Ramacandra observed complete celibacy and performed an uninterrupted Agnihotra-yajña for thirteen thousand years.
Srimad Bhagavatam Canto 09, Chapter 11, Text 17
Srimad Bhagavatam Canto 09, Chapter 11, Text 19