What did Umar (RA) do when he observed people praying two rakahs after the 'Asr prayer, as mentioned in the hadith of Anas b. Malik regarding the voluntary prayers after the afternoon prayer that the Prophet Muhammad (saw) saw, but neither commanded nor forbade?
 Mukhtar b. Fulful said:                      I asked Anas b. Malik about the voluntary prayers after the afternoon prayer, and he replied: 'Umar struck hit hands on prayer observed after the 'Asr prayer and we used to observe two rak'ahs after the sun set before the evening prayer during the time of the Apostle of Allah (may peace be upon him). I said to him: Did the Messenger of Allah (may peace be upon him) observe them? He said: He saw us observing them, but he neither commanded us nor forbade us to do so.