How to phrase "You know what they say? [quote]" in Chinese? When giving some kind of saying or folklore knowledge, in English we often say e.g.:

You know what they say?  Two heads are better than one.

I want to say something similar in Chinese:

You know what they say?  天不怕地不怕，就怕老外说中国话！

I find this an amusing rhyme, and it usually gets a laugh.  However, I'm not sure what to preface it with.  YouDao uses semi-literal translations:

你知道他们说...
Nǐ zhīdào tāmen shuō...
你知道他们怎么说...
Nǐ zhīdào tāmen zěnme shuō...

But I don't know if this is actually used by Chinese speakers (outside of translations from English).  Perhaps it's Engnese (reverse Chinglish) to say this, and there's a more appropriate phrase in Chinese.
Question: How to phrase &quot;You know what they say? [quote]&quot; in Chinese?
你知道他们说的什么吗

你知道他们怎么说吗

are common phrases， but not for this context。

Depends on the type of the quote， you can use

俗话说/老话说/有句话叫：folk saying

古语有云 （classical saying）

X曰 （quote from ancient scholar）

XX说 （common phrase）

A: 俗话说： 三个臭皮匠， 顶一个诸葛亮（Two heads are better than one）

B：有句话叫： 人多手乱。

A：古人云：多多益善。

B：子曰：你说得不对。

A: 高尔基说： 子没说过。