Humran bin Aban narrates from Sayyiduna Mu'awiyah (may Allah be pleased with him) that he said: "You pray a prayer that we never saw the Prophet (peace and blessings be upon him) pray; indeed, he (peace and blessings be upon him) forbade praying two rak'ahs after Asr."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4375