The Book of Prayers (Kitab Al-Salat)

Muslim :: Book 4 : Hadith 1266

Abu Huraira reported: The Messenger of Allah (may peace be upon him) said: He who finds (gets) a rak'ah of the afternoon (prayer) before the setting of the sun, he in fact gets (the full prayer), and he who gets a rak'ah of the morning (prayer) before the rising of the sun he in fact gets (the full prayer).