It is narrated from Sayyiduna Sa’d bin Abi Waqqas (may Allah be pleased with him), the Messenger of Allah (peace and blessings be upon him) said: There are two prayers after which no further prayer is to be performed: one is the Fajr prayer, until the sun rises, and the other is the Asr prayer, until the sun sets.
Hadith Referenceالفتح الربانی / كتاب الصلاة / 1201