Sahih Bukhari Volume 1, Book 8, Hadith Number 437
Narated By ‘Abdullah bin ‘Umar : In the life-time of Allah’s Apostle the mosque was built of adobes, its roof of the leaves of date-palms and its pillars of the stems of date-palms. Abu Bakr did not alter it. ‘Umar expanded it on the same pattern as it was in the lifetime of Allah’s Apostle by using adobes, leaves of date-palms and changing the pillars into wooden ones. ‘Uthman changed it by expanding it to a great extent and built its walls with engraved stones and lime and made its pillars of engraved stones and its roof of teak wood.