Mukhtasar Bukhari (Abridged) 344 — Catching one rak’ah of Asr before

Narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When any one of you gets one rak'ah of the Asr prayer before the sun sets, he should complete his prayer, and when he gets one rak'ah of the Fajr prayer before the sun rises, he should (also) complete his prayer."