I heard Sayyiduna Abu Umamah (may Allah be pleased with him) say: We offered the Zuhr prayer with Umar bin Abd al-Aziz (may Allah have mercy on him), then we went out (of the mosque) and came to Sayyiduna Anas bin Malik (may Allah be pleased with him). We saw that he was offering the Asr prayer. I asked: (O uncle!) "Which prayer is this that you are offering at this time?" He said: "This is the Asr prayer, and this is the prayer of the Messenger of Allah (peace and blessings be upon him) which we used to offer with him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2087