(41) CHAPTER. Can the Imam offer the Salat (prayer) with only those who are present (for the prayer)? And can he deliver a Khutba (religious talk) on Friday if it is raining?
Narrated Abu Sa`id Al-Khudri: A cloud came and it rained till the roof started leaking and in those days the roof used to be of the branches of date-palms. Iqama was pronounced and I saw Allah's Apostles prostrating in water and mud and even I saw the mark of mud on his forehead.
Authentic