Reading Clive's argument that G1 etc never had been cladded with casing blocks reminded me to re-read 'Cairo - Biography of a City' J.Aldrige ( 1969) which mentions the pyramids and the construction of Cairo's more famous buildings.
I thought that earthquakes were the usual argument for the pyramids being used to supply stone for the re-building of Cairo, but although this book does mention earthquakes separately elsewhere it does not relate the pyramids and Cairo earthquakes.
It gives Saladin as the ruler who built the Citadel with stone stripped from the "small Pyramid" in approx 1169- 1180.
It says that the Hasan Mosque was built from stone taken from the pyramids " The first impression is simply of its size. Its walls from the street are sheer, 113feet high built of beautifully cut stone brought from the pyramids" p120.

Don't know how accurate this book is but it seems well researched and the author lived in Cairo for many years.