Maliks Muwatta Book 1, Hadith Number 5.

Section : The Times of Prayer.

Yahya related to me from Malik from Zayd ibn Aslam from Ata ibn Yasar and from Busr ibn Said and from al-Araj-all of whom related it from Abu Hurayra – that the Messenger of Allah, may Allah bless him and grant him peace, said, “Whoever manages to do a raka of subh before the sun has risen has done subh in time, and whoever manages to do a raka of asr before the sun has set has done asr in time.”