Sahih Bukhari Volume 002, Book 022, Hadith Number 325.
Narated By Kuraib : I was sent to 'Aisha by Ibn Abbas, Al-Miswar bin Makhrama and 'Abdur-Rahman bin Azhar. They told me to greet her on their behalf and to ask her about the offering of the two Rakat after the 'Asr prayer and to say to her, "We were informed that you offer those two Rakat and we were told that the Prophet had forbidden offering them." Ibn Abbas said, "I along with 'Umar bin Al-Khattab used to beat the people whenever they offered them." I went to 'Aisha and told her that message. 'Aisha said, "Go and ask Um Salama about them." So I returned and informed them about her statement. They then told me to go to Um Salama with the same question with which t sent me to 'Aisha. Um Salama replied, "I heard the Prophet forbidding them. Later I saw him offering them immediately after he prayed the 'Asr prayer. He then entered my house at a time when some of the Ansari women from the tribe of Bani Haram were sitting with me, so I sent my slave girl to him having said to her, 'Stand beside him and tell him that Um Salama says to you, "O Allah's Apostle! I have heard you forbidding the offering of these (two Rakat after the 'Asr prayer) but I have seen you offering them." If he waves his hand then wait for him.' The slave girl did that. The Prophet beckoned her with his hand and she waited for him. When he had finished the prayer he said, "O daughter of Bani Umaiya! You have asked me about the two Rakat after the 'Asr prayer. The people of the tribe of 'Abdul-Qais came to me and made me busy and I could not offer the two Rakat after the Zuhr prayer. These (two Rakat that I have just prayed) are for those (missed) ones.