מדרש על סנהדרין 200:5

י) "The watchman does not sleep. When she is a minor- lest she be seduced or raped in her youth. When she has grown up- lest she commit adultery." (see Sanhedrin 100b) He said to him, "Everything that you have said, you have said truly." He said to him, "Say 'Kaf.'" He said to him: