The Messenger of Allah ﷺ said, "The night prayer is two by two, and if you fear the approach of dawn, then conclude with a single witr unit."I asked, "What does 'two by two' mean?"He answered, "Two units at a time, two units at a time."
حدثنا بهز حدثنا شعبة أخبرني عقبة سمعت
قال رسول الله ﷺ صلاة الليل مثنى مثنى فإن خشيت الصبح فأوتر بركعة قال قلت ما مثنى مثنى قال ركعتان ركعتان