It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: “Whoever catches one rak‘ah of the Fajr prayer before the sun rises has certainly caught the Fajr prayer, and whoever catches one rak‘ah of the ‘Asr prayer before the sun sets has caught the ‘Asr prayer.”
Hadith Referenceالسنن المأثورة / باب ما جاء في الصلاة على الراحلة / 108
Hadith Takhrijصحیح مسلم، المساجد ومواضع الصلاة باب ومن ادرك ركعة من الصلاة فقد ادرك تلك الصلاة، رقم : 608۔