Srimad Bhagavatam Canto 04, Chapter 19, Text 11

SB 4.19.11

caramenasvamedhena
yajamane yajus-patim
vainye yajña-pasum spardhann
apovaha tirohitah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
 
When Prthu Maharaja was performing the last horse sacrifice [asvamedha-yajña], King Indra, invisible to everyone, stole the horse intended for sacrifice. He did this because of his great envy of King Prthu.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
 
King Indra is known as sata-kratu, which indicates that he has performed one hundred horse sacrifices (asvamedha-yajña). We should know, however, that the animals sacrificed in the yajña were not killed. If the Vedic mantras were properly pronounced during the sacrifice, the animal sacrificed would come out again with a new life. That is the test for a successful yajña. When King Prthu was performing one hundred yajñas, Indra became very envious because he did not want anyone to excel him. Being an ordinary living entity, he became envious of King Prthu, and, making himself invisible, he stole the horse and thus impeded the yajña performance.
Srimad Bhagavatam Canto 04, Chapter 19, Text 10
Srimad Bhagavatam Canto 04, Chapter 19, Text 12