Jābir (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) was asked: "Which part of the prayer is the best?" He replied: "The long standing."
The Prophet (may Allah's peace and blessings be upon him) was asked what actions in the prayer were the best. They asked this for their eagerness to achieve the most amount of rewards. They meant which part of prayer e.g, bowing or prostration is the best? He answered that it was the long standing in the prayer.