Alqamah bin Waqas Laithi (may Allah have mercy on him) says that I asked Hazrat Aisha (may Allah be pleased with her) how the Prophet (peace and blessings of Allah be upon him) used to perform two rak'ahs while sitting. She replied that the Prophet (peace and blessings of Allah be upon him) used to recite (Qur'an) while sitting, but when he intended to bow (ruku'), he would stand up and then perform the bowing.