SB 9.6.50
aho imam pasyata me vinasam
tapasvinah sac-carita-vratasya
antarjale vari-cara-prasangat
pracyavitam brahma ciram dhrtam yat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Alas! While practicing austerity, even within the depths of the water, and while observing all the rules and regulations practiced by saintly persons, I lost the results of my long austerities simply by association with the sexual affairs of fish. Everyone should observe this falldown and learn from it.