What should a person who has performed ablution do if, immediately after completing the ablution, they discover a very small spot that water did not reach? Should they repeat the ablution or merely moisten that spot?

If someone performing ablution forgets to wash a part of their limbs and remembers it soon after, they should wash only the forgotten part and what comes after it with the intention of ablution. They are not required to repeat the entire ablution, because the sequence in ablution is obligatory. For example, if they forgot to wash their left hand and remembered after washing their feet, they should wash their left hand, then wipe their head and ears, and then wash their feet.