Sayyidah Aishah (may Allah be pleased with her) said that the Prophet (peace and blessings be upon him) himself used to pray two rak'ahs after Asr and used to forbid others from it, and he himself used to observe continuous fasting (sawm al-wisal) and forbade others from continuous fasting.
(b) In this, and in some of what has preceded, there is an indication that continuing these two rak'ahs, after the making-up that took place in the house of Sayyidah Umm Salamah (may Allah be pleased with her), was particular to the Prophet (peace and blessings be upon him). Sayyidah Aishah (may Allah be pleased with her) said that the Prophet (peace and blessings be upon him) forbade "that one should wait for the rising or setting of the sun." (When Sayyidah Aishah (may Allah be pleased with her) saw the constancy of the Prophet (peace and blessings be upon him), she applied it to these two times only, whereas the prohibition is established both at these two times and before them; so the correct view is that this was particular to the Prophet (peace and blessings be upon him), and Allah knows best. And a narration has also been reported from Sayyiduna Ali (may Allah be pleased with him), from the Prophet (peace and blessings be upon him), which indicates that it is permissible if Asr has been prayed at the beginning of its time.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4402