(60) باب وَقْتِ رَكْعَتَىِ الْفَجْرِ وَذِكْرِ الاِخْتِلاَفِ عَلَى نَافِعٍ
It was narrated that Ibn 'Abbas said:
"The Prophet (ﷺ) used to pray two rak'ahs of Fajr when he heard the Adhan and he made them brief." (IT)
Reference (IT): Sunan an-Nasa'i 1782 (IT)
In-book reference (IT): Book 20, Hadith 185 (IT)
English translation (IT): Vol. 2, Book 20, Hadith 1783 (IT)