Masjid al-Nabawi

To understand the origins and form of Islamic architecture, we need to understand the  importance of the function and design of the Prophet Muhammad's house in Medina.  The diagram below from Robert Hillenbrand's study of Islamic architecture is based on various hadiths and memoirs of the Prophet Muhammad's life and enough details emerged that allow scholars to provide a conjectural representation of the space and layout of the house. 

Source:  Robert Hillenbrand, Islamic Architecture:  Form, function and meaning. (New York: Columbia University Press, 1994), 39

Here is a hadith on the building of the mosque

The house was notable for its expansive size and particularly the dimensions of the courtyard.  As the Prophet Muhammad gained followers and people converted to Islam, the sense of the umma أمة  or people who could meet and pray together became a feature of the courtyard as it became in effect the very first mosque.  The form of the Prophet's house then became a prototype for early mosque architecture that became very influential and widespread.

The main features of the house are important for us to discern as a vocabulary of Islamic elements of architecture. The enclosing walls were plain.  Along the inner wall facing the qibla was the zulla, or shaded place, a double row of palm trunks carrying a roof of palm leaves plastered with mud.  This feature was apparently added because some of the early Companions of the Prophet, the sahaba, needed shade while at prayer.  (Hillenbrand, 40)

Dome of the Rock, in Jersusalem the qibla originally faced toward Jerusalem, but as a result of divine revelation, the Prophet Muhammad changed the qibla to face the Ka'ba at Mecca. 

The form of the masjid shown here is known as a hypostyle mosque.  The hypostyle is used to describe mosques that have the following elements:
1.  A building or structure with a roof supported by columns.  This may also be seen as the riwaq or covered roof area along the wall.  
2.  It commonly has an enclosing set of walls
2.  A large open sahn or courtyard found within the walls to enclose or gather the umma
3.  A qibla wall marking the direction of prayer toward Mecca

2

Prayer (Kitab Al-Salat)

(161)

Chapter: On (The Reward) Of Building Masajid

(12)

باب فِي بِنَاءِ الْمَسَاجِدِ

Source:  Wikipedia

'Abd Allah b. 'Umar reported:

The mosque (of the Prophet) during his lifetime was built with bricks, its roof with branches of the palm-tree, and its pillars with palm-wood, as Mujahid said: Abu Bakr did not add anything to it. But 'Umar added to it; he built as it was built during the lifetime of the Messenger of Allah (ﷺ) with bricks and branches, and he changed its pillars. Mujahid said: Its pillars were made of wood. 'Uthman changed it altogether with increasing addition. He built its walls with decorated stone and lime. And he built the pillars with decorated stone and its roof with teak. Mujahid said: Its roof was made of teak.

Abu Dawud said: Al-Qassah means lime used as mortar.

حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى بْنِ فَارِسٍ، وَمُجَاهِدُ بْنُ مُوسَى، - وَهُوَ أَتَمُّ - قَالاَ حَدَّثَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا أَبِي، عَنْ صَالِحٍ، حَدَّثَنَا نَافِعٌ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، أَخْبَرَهُ أَنَّ الْمَسْجِدَ كَانَ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم مَبْنِيًّا بِاللَّبِنِ وَالْجَرِيدِ - قَالَ مُجَاهِدٌ وَعَمَدُهُ مِنْ خَشَبِ النَّخْلِ - فَلَمْ يَزِدْ فِيهِ أَبُو بَكْرٍ شَيْئًا وَزَادَ فِيهِ عُمَرُ وَبَنَاهُ عَلَى بِنَائِهِ فِي عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم بِاللَّبِنِ وَالْجَرِيدِ وَأَعَادَ عَمَدَهُ - قَالَ مُجَاهِدٌ عُمُدَهُ خَشَبًا - وَغَيَّرَهُ عُثْمَانُ فَزَادَ فِيهِ زِيَادَةً كَثِيرَةً وَبَنَى جِدَارَهُ بِالْحِجَارَةِ الْمَنْقُوشَةِ وَالْقَصَّةِ وَجَعَلَ عَمَدَهُ مِنْ حِجَارَةٍ مَنْقُوشَةٍ وَسَقَّفَهُ بِالسَّاجِ ‏.‏ قَالَ مُجَاهِدٌ وَسَقْفُهُ السَّاجُ ‏.‏ قَالَ أَبُو دَاوُدَ الْقَصَّةُ الْجِصُّ ‏.‏