Bulugh al-Maram

Narrated Anas (rad): The Companions of Allah’s Messenger (ﷺ) in his lifetime used to wait for the ‘Isha (night) prayer, so much so that their heads were lowered down (by dozing). They would then pray without performing ablution. [Reported by Abu Da’ud and Ad-Daraqutni graded it Sahih (sound). Its origin is in Muslim].