Mathew 7:6 is as per Bible Study directly related to the verse that you quoted. You would know that if you had studied The Holy Bible.
& FYI, it is used for when someone tries to abuse a Bible verse for "not GOoD reasons".
Here is another one, look up the root of the word good. You may be surprised just how often everyone who speaks English is actually confirming The Holy Bible, without even knowing it!