From Sahih Bukhari (Hadith 669):
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 Messenger (ﷺ) prostrating in water and mud and even I saw the mark of mud on his forehead
Reference: Bukhari 669