Sahih Bukhari: Hadith 440

In the lifetime of Allah's Messenger (ﷺ) 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 Messenger (ﷺ) 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.