The Messenger of Allah ﷺ saw a man praying the two rakahs before the dawn prayer while he himself was already in the prayer. When he had finished, he asked the man, "Which of your two prayers did you count?"
حدثنا أبو بكر بن أبي شيبة حدثنا أبو معاوية عن عاصم
أن رسول الله ﷺ رأى رجلا يصلي الركعتين قبل صلاة الغداة وهو في الصلاة فلما صلى قال له بأي صلاتيك اعتددت
No references are available.
Muslim narrated it in "Prayer of the Traveler," the preceding chapter, no. 712, from the hadith of Abu Muawiya and others through this route.