This is what the website says. It was August 6th, not 14th.
15) August 6 2001. Memo. President George Bush receives an intelligence briefing, titled “Bin Laden determined to strike in the U.S.” that warned that "bin Laden may attempt to " hijack airplanes."
(Eggen and Woodward 5-18-2002; CBS News 5-16-2002; Boncombe 5-19-2002).
(the information in quotes are from news shows that ran features on this memo).
Here is the webpage it is from. This is not the ONLY webpage. This is a well known FACT.