What are the consequences of leaving the trace of urine—which exited after relieving oneself due to movement—to dry without cleansing it, given that ritual purity is not obligatory for prayer at that time?

If urine or prostatic fluid (wadi) gets on clothes or the body, the contaminated area must be washed even if it has dried. Impurity is removed by washing, by pouring water over it until its substance (color, smell, or trace) disappears, and mere sprinkling is not sufficient. There is no specific amount of water required for washing; rather, it is sufficient that the water covers the impurity and removes it.