풍문으로 들었소. I heard it by hearsay

I know it by hearsay.

I have (got) it by hearsay.

I heard it through[on] the grapevine.

I heard through[on] the grapevine that you're moving to New York. Is it true?

I got it straight from the horse's mouth that Vivian would get a divorce. 

It came straight from the horse's mouth. 

safe source. 

I have gotten the information from the horses themselves and the info is the correct!

말에게서 직접 들은 정보가 있네. 그러니 그만큼 정확할 수 밖에! 라고 호언장담한 데서 비롯됐다.

the correct에서 the는 부사로 '그만큼'이라는 의미이다.