Must I repeat the entire ablution, or only wash the part I am unsure about, if I doubt having washed a part of my left foot immediately after completing the ablution?

The questioner is advised to ignore obsessive doubts so that they do not intensify and prevent him from performing worship. If someone doubts the complete coverage of a limb during ablution (wudu'), he should ensure its complete coverage and remove the doubt. However, if he doubts after completing the ablution, he is not required to repeat it, especially if he is prone to obsessive doubts. The principle is that a Muslim performs a complete ablution and does not pay attention to doubts. If the doubt is concerning the washing of the left foot (the last limb in ablution), there is no harm in washing it again with a new intention to remove the doubt.