Musnad Ahmad 1153:1621

Ibrahim ibn Khalid narrated to us, Rabah narrated to us, from Ma'mar, from Ibn Tawus, from his father, from Aisha, that she said: "The Messenger of Allah, peace and blessings of Allah be upon him, did not abandon the two rak'ahs after the Asr prayer." She said: And the Messenger of Allah, peace and blessings of Allah be upon him, said: "And do not seek to pray at the rising of the sun, nor at its setting, so that you pray at that time."