كتاب الفضائل
8
The Book of Virtues
(197)
Chapter: Briefness to be Adopted in Performing the two Rak'ah Sunnah before Fajr Prayer, their time and the Surah to recite in them
(197)
- باب تخفيف ركعتي الفجر وبيان ما يقرأ فيهما، وبيان وقتهما‏.
Riyad as-Salihin 1106
Ibn 'Umar (May Allah be pleased with them) reported:
The Messenger of Allah (ﷺ) used to perform his optional night prayers at night, two Rak'ah followed by two Rak'ah, and at the end he would conclude with an odd Rak'ah (Witr). Then he would perform two Rak'ah prayer before the dawn (Fajr) prayer after hearing the Adhan, and he would make them so brief as if he could hear the Iqamah being called.

[Al- Bukhari and Muslim].

وعن ابن عمر رضي الله عنهما قال‏:‏ كان رسول الله صلى الله عليه وسلم يصلي من الليل مثنى مثنى، ويوتر بركعة من آخر الليل، ويصلي الركعتين قبل صلاة الغداة، وكأن الأذان بأذنيه‏"‏‏.‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏
Reference : Riyad as-Salihin 1106
In-book reference : Book 8, Hadith 116