(5) باب إِذَا أَدْرَكَ الإِمَامَ وَلَمْ يُصَلِّ رَكْعَتَىِ الْفَجْرِ
Narrated 'Abd Allah b. Sarjas:
A man came while the Prophet (ﷺ) was leading the people in the dawn prayer. He prayed the two rak'ahs and then joined the congregational prayer led by the Prophet (ﷺ). When he finished the prayer, the Prophet (ﷺ) said: So-and-so, which was your real prayer, the one you prayed alone or the one offered with us ?
Reference: Sunan Abi Dawud 1265
In-book reference: Book 5, Hadith 16
English translation: Book 5, Hadith 1260