ואמר ר' שפטיה אמר ר' יוחנן מנין שמשתמשין בבת קול שנאמר (ישעיהו ל, כא) ואזניך תשמענה דבר מאחריך לאמר והני מילי דשמע קל גברא במתא וקל איתתא בדברא והוא דאמר הין הין והוא דאמר לאו לאו
And Rabbi Shefatya said that Rabbi Yoḥanan said: If one was deliberating about whether to do a certain action, and a Divine Voice indicated what he should do, from where is it derived that one may make use of a Divine Voice and rely upon it? As it is stated: “And your ears shall hear a word behind you saying: This is the way, walk in it” (Isaiah 30:21). The Gemara comments: This applies only when one heard a male voice in the city, which is unusual, for men are usually found in the fields, or when one heard a female voice in the fields, for women are generally not found there. Since the voice is unusual, one need not doubt it and may rely upon it. And that applies when the voice repeated its message and said: Yes, yes. And that also applies when the voice said: No, no.
Guide for the Perplexed 2:42:
The bat-kol (prophetic echo), which is so frequently mentioned by our Sages, and is something that may be experienced by men not prepared for prophecy.
For dozens of references regarding the bas kol spanning all of Jewish literature please see this web-page.