Hisham bin Hujayr (may Allah have mercy on him) said: Tawus (may Allah have mercy on him) used to pray two rak'ahs after Asr. Ibn Abbas (may Allah be pleased with them both) said to him: Leave them. Tawus (may Allah have mercy on him) said: The Messenger of Allah (peace and blessings be upon him) forbade them "only lest they be taken as a ladder."
Ibn Abbas (may Allah be pleased with them both) said: The Prophet (peace and blessings be upon him) "forbade praying after Asr." I do not know whether you will be rewarded or punished for them, because Allah says: "It is not for a believing man or a believing woman, when Allah and His Messenger have decided a matter, that they should have any choice in their affair." [Surah al-Ahzab: 36]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4377