Ata ibn Yasar عطاء بن يسار أبو محمد مولى ميمونة · The Book on Salat (Prayer)

the Prophet said: "Whoever catches a Rak'ah of Subh before the sun has risen, then he has caught Subh. Whoever catches a Rak'ah of Asr before the sun has set, then he has caught Asr."

Allah's Messenger (S) said: "When one of you prays the two Rak'ah of Fajr then let him lay down on his right (side)."