(61) باب فِيمَنْ يُصَلِّي رَكْعَتَىِ الْفَجْرِ وَالإِمَامُ فِي الصَّلاَةِ
It was narrated that 'Abdullah bin Sarjis said:
"A man came while the Messenger of Allah (ﷺ) was praying Subh, and he prayed two Rak'ahs then joined the prayer. When the Messenger of Allah (ﷺ) had finished praying he said: O so-and-so, which of them is your prayer - the one you prayed withus or the one you prayed on your own?"'
Reference: Sunan an-Nasa'i 868
In-book reference: Book 10, Hadith 92
English translation: Vol. 1, Book 10, Hadith 869