Reference for Berakhot 43:19

אמר ריב"ל מה טיבן של טובלי שחרין מה טיבן הא איהו דאמר בעל קרי אסור בדברי תורה הכי קאמר מה טיבן בארבעים סאה אפשר בתשעה קבין מה טיבן בטבילה אפשר בנתינה

R. Joshua b. Levi said : What is the purpose of those [who are Ba'al Keri] who bathe in the morning ? What is their purpose ! And it was he who said that a Ba'al Keri is forbidden to be engaged with words of Torah ! Nay, this is what he means to say : What is their purpose in using forty Saot of water, when it is possible [to become clean] with nine Kabs? What is their purpose in undergoing complete immersion when it is possible [to become clean] with water poured over one ?

Jastrow