Muwatta Malik Book 7, Hadith 30
Malik related to me from Yahya ibn Said that A'isha, the wife of
the Prophet, may Allah bless him and grant him peace, said, "The
Messenger of Allah, may Allah bless him and grant him peace, used to
pray the two rakas of the dawn (fajr) so quickly that I would say to
myself 'Has he recited the umm al-Qur'an or not?' "
Yahya related to me from Malik from Nafi from Abdullah ibn Umar that Hafsa, the wife of the Prophet, may Allah bless him and grant him peace, told him that the Messenger of Allah, may Allah bless him and grant him peace, used to pray two quick rakas when the muadhdhin had finished the adhan for the subh prayer, before the iqama was said for the prayer.
Yahya related to me from Malik from Sharik ibn Abdullah ibn Abi Namir that Abu Salama ibn Abd ar-Rahman said, "Some people heard the iqama and started to pray. The Messenger of Allah, may Allah bless him and grant him peace, came out and said, 'Are you doing two prayers at the same time? Are you doing two prayers at the same time?' That was about the subh prayer and the two rakas before subh."